Substrates carrying polymers of linked sandwich coordination compounds and methods of use thereof

ABSTRACT

The present invention provides high density, non-volatile memory devices incorporating polymers comprised of sandwich coordination compounds. Such polymers can have multiple different and distinguishable oxidation states (e.g., ten different and distinguishable oxidation states), and thus provide molecules, information storage media and apparatus that store multiple bits of information. In addition, the polymers can be immobilized or bound to a substrate to produce other useful articles, such as electrochromic displays, molecular capacitors, and batteries.

RELATED APPLICATIONS

This application is divisional of commonly owned, application Ser. No.09/605,587, filed Jun. 28, 2000, U.S. Pat. No. 6,451,942 which is inturn a continuation-in-part of commonly owned application Ser. No.09/483,500 of Jonathan S. Lindsey, filed Jan. 14, 2000, now issued asU.S. Pat. No. 6,212,093, the disclosures of both of which areincorporated by reference herein in their entirety.

This invention was made with Government support under Grant No.N00014-99-1-0357 from the Office of Naval Research. The Government hascertain rights to this invention.

FIELD OF THE INVENTION

This invention relates to the articles of manufacture comprising asubstrate having electric storage molecules bound thereto, along withmethods of use thereof.

BACKGROUND OF THE INVENTION

Basic functions of a computer include information processing andstorage. In typical computer systems, these arithmetic, logic, andmemory operations are performed by devices that are capable ofreversibly switching between two states often referred to as “0” and“1”. In most cases, such switching devices are fabricated fromsemiconducting devices that perform these various functions and arecapable of switching between two states at a very high speed usingminimum amounts of electrical energy. Thus, for example, transistors andtransistor variants perform the basic switching and storage functions incomputers.

Because of the huge data storage requirements of modern computers, anew, compact, low-cost, very high capacity, high speed memoryconfiguration is needed. To reach this objective, molecular electronicswitches, wires, microsensors for chemical analysis, and opto-electroniccomponents for use in optical computing have been pursued. The principaladvantages of using molecules in these applications are high componentdensity (upwards of 10¹⁰ bits per square centimeter), increased responsespeeds, and high energy efficiency.

A variety of approaches have been proposed for molecular-based memorydevices. While these approaches generally employ molecular architecturesthat can be switched between two different states, all of the approachesdescribed to date have intrinsic limitations making their uses incomputational devices difficult or impractical.

For example, such approaches to the production of molecular memorieshave involved photochromic dyes, electrochromic dyes, redox dyes, andmolecular machines, all having fundamental limitations that haveprecluded their application as viable memory elements. These moleculararchitectures are typically limited by reading/writing constraints.Furthermore, even in cases where the effective molecular bistability isobtained, the requirement for photochemical reading restricts the devicearchitecture to a 2-dimensional thin film. The achievable memory densityof such a film is unlikely to exceed 10¹⁰ bits/cm². Such limitationsgreatly diminish the appeal of these devices as viable molecular memoryelements.

SUMMARY OF THE INVENTION

The present invention provides a polymer comprising or consisting of aplurality of covalently joined monomeric units, the monomeric unitscomprising sandwich coordination compounds. The covalently joinedmonomeric units in the polymer may be the same sandwich coordinationcompounds (e.g., the polymer is a homopolymer) or different sandwichcoordination compounds (e.g., the polymer is a copolymer). The polymersmay be covalently bound (direct or through a linker) or noncovalentlybound (via ionic linkage or non-ionic “bonding”, etc.) to a substrate (acarrier substrate) to produce an article of manufacture. The substratemay be any of a variety of materials, including conductors,semiconductors, insulators, and composites thereof. Particular materialsinclude metals, metal oxides, organic polymers, etc. The polymers may bebonded singly or co-deposited with one or more other polymers and/orother information storage molecules.

Such articles of manufacture are useful for a variety of purposes. Forexample, these polymers and articles of manufacture afford promisingelectrochromic display materials, potentially offering high contrast anda wide variety of colors by tuning the applied electric potential. Thesematerials also find potential applications as intrinsic molecularsemiconductors. The rich electrochemical properties of these materialsalso make them useful as potential battery materials and forapplications in molecular-based information storage devices.

Polymers of the present invention may be represented by Formula I:

X¹X^(m+1))_(m)  (I)

wherein:

m is at least 1 (e.g., 1, 2, or 3 to 10, 20, 50 or 100 or more); and

X¹ through X^(m+1) are sandwich coordination compounds (each of whichmay be the same or different).

Specific examples of polymers of Formula I are polymers of Formula II:.

X¹—Y¹—X²—Y²—X³—Y³—X⁴—Y⁴—X⁵—Y⁵—X⁶—Y⁶—X⁷—Y⁷—X⁸—Y⁸—X⁹—Y⁹—X¹⁰  (II)

wherein:

X¹ through X¹⁰ are each independently selected sandwich coordinationcompounds;

Y¹ through Y⁹ are independently selected linking groups or linkers; and

X³ through X¹⁰ (and Y³ through Y⁹) may each independently orconsecutively be present or absent (e.g., to provide a polymer ofanywhere from 2 to 10 sandwich coordination compounds)

Articles of manufacture of the present invention may be represented byFormula III:

A—X¹(X^(m+1))_(m)  (III)

wherein:

A is a substrate (e.g., a conductor, a semiconductor, an insulator, or acomposite thereof);

m is at least 1 (e.g., 1, 2, or 3 to 10, 20, 50 or 100 or more); and

X¹ through X^(m+1) are sandwich coordination compounds (each of whichmay be the same or different).

Specific examples of articles of manufacture of Formula III are articlesof Formula IV:

A-X¹—Y¹—X²—Y²—X³—Y³—X⁴—Y⁴—X⁵—Y⁵—X⁶—Y⁶—X⁷—Y⁷—X⁸—Y⁸—X⁹—Y⁹—X¹⁰  (IV)

wherein:

A is a substrate (e.g., a conductor, a semiconductor, an insulator, or acomposite thereof);

X¹ through X¹⁰ are each independently selected sandwich coordinationcompounds;

Y¹ through Y⁹ are independently selected linking groups or linkers; and

X³ through X¹⁰ (and Y³ through Y⁹) may each independently orconsecutively be present or absent (e.g., to provide a polymer ofanywhere from 2 to 10 sandwich coordination compounds)

Particular examples of sandwich coordination compounds that may be usedto carry out the present invention have the Formula XI (fordouble-decker sandwich compounds) or Formula XII (for triple-deckersandwich compounds):

wherein:

M¹ and M² (when present) are metals independently selected from thegroup consisting of metals of the lanthanide series (Ln=La, Ce, Pr, Nd,Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, as well as Y, Zr, Hf, andBi, and in the actinide series Th and U (radioactive elements such as Pmare generally less preferred);

L¹, L² and L³ (when present) are independently selected ligands (e.g.,porphyrinic macrocycles); and

Q¹, Q² and Q³ may be present or absent and when present areindependently selected linkers (the linker preferably including aprotected or unprotected reactive group such as thio, seleno or tellurogroup). Preferably, at least one of Q¹, Q², and Q³ is present.

In one particular embodiment, this invention provides an apparatus forstoring data (e.g., a “storage cell”). The storage cell includes a fixedelectrode electrically coupled to a “storage medium” comprising apolymer as described above, the polymer having a plurality of differentand distinguishable oxidation states where data is stored in the(preferably non-neutral) oxidation states by the addition or withdrawalof one or more electrons from said storage medium via the electricallycoupled electrode.

In preferred storage cells, the storage medium stores data at a densityof at least one bit, and preferably at a density of at least 2 bits.Thus, preferred storage media have at least 2, and preferably at least4, 8 or 10 or more different and distinguishable oxidation states. Inparticularly preferred embodiments, the bits are all stored innon-neutral oxidation states. In a most preferred embodiment, thedifferent and distinguishable oxidation states of the storage medium canbe set by a voltage difference no greater than about 5 volts, morepreferably no greater than about 2 volts, and most preferably no greaterthan about 1 volt.

The storage medium is electrically coupled to the electrode(s) by any ofa number of convenient methods including, but not limited to, covalentlinkage (direct or through a linker), ionic linkage, non-ionic“bonding”, simple juxtaposition/apposition of the storage medium to theelectrode(s), or simple proximity to the electrode(s) such that electrontunneling between the medium and the electrode(s) can occur. The storagemedium can contain or be juxtaposed to or layered with one or moredielectric material(s). Preferred dielectric materials are imbedded withcounterions (e.g. Nafion® fluoropolymer). The storage cells of thisinvention are fully amenable to encapsulation (or other packaging) andcan be provided in a number of forms including, but not limited to, anintegrated circuit or as a component of an integrated circuit, anon-encapsulated “chip”, etc. In some embodiments, the storage medium iselectronically coupled to a second electrode that is a referenceelectrode. In certain preferred embodiments, the storage medium ispresent in a single plane in the device. The apparatus of this inventioncan include the storage medium present at a multiplicity of storagelocations, and in certain configurations, each storage location andassociated electrode(s) forms a separate storage cell. The storagemedium may be present on a single plane in the device (in a twodimensional or sheet-like device) or on multiple planes in the device(in a three-dimensional device). Virtually any number (e.g., 16, 32, 64,128, 512, 1024, 4096, etc.) of storage locations and storage cells canbe provided in the device. Each storage location can be addressed by asingle electrode or by two or more electrodes. In other embodiments, asingle electrode can address multiple storage locations and/or multiplestorage cells.

In preferred embodiments, one or more of the electrode(s) is connectedto a voltage source (e.g. output of an integrated circuit, power supply,potentiostat, microprocessor (CPU), etc.) that can provide avoltage/signal for writing, reading, or refreshing the storage cell(s).One or more of the electrode(s) is preferably connected to a device(e.g., a voltammetric device, an amperometric device, a potentiometricdevice, etc.) to read the oxidation state of said storage medium. Inparticularly preferred embodiments, the device is a sinusoidalvoltammeter. Various signal processing methods can be provided tofacilitate readout in the time domain or in the frequency domain. Thus,in some embodiments, the readout device provides a Fourier transform (orother frequency analysis) of the output signal from said electrode. Incertain preferred embodiments, the device refreshes the oxidation stateof said storage medium after reading said oxidation state.

Particularly preferred methods and/or devices of this invention utilizea “fixed” electrode. Thus, in one embodiment, methods and/or devices inwhich the electrode(s) are moveable (e.g. one or more electrodes is a“recording head”, the tip of a scanning tunneling microscope (STM), thetip of an atomic force microscope (AFM), or other forms in which theelectrode is movable with respect to the storage medium) are excluded.Similarly in certain embodiments, methods and/or devices and/or storagemedia, in which the storage molecules are responsive to light and/or inwhich the oxidation state of a storage molecule is set by exposure tolight are excluded.

In another embodiment, this invention provides an information storagemedium. The information storage medium can be used to assemble storagecells and/or the various memory devices described herein. In a preferredembodiment the storage medium comprises one or more different storagemolecules. When different species of storage molecule are present, theoxidation state(s) of each species is preferably different from anddistinguishable from the oxidation state(s) of the other species ofstorage molecule comprising the storage medium.

This invention also provides methods of storing data. The methodsinvolve i) providing an apparatus, e.g., comprising one or more storagecells as described herein; and ii) applying a voltage to the electrodeat sufficient current to set an oxidation state of said storage medium(the storage medium comprising one or more storage cells). In preferredembodiments, the voltage range is less than about 5 volts, morepreferably less than about 2 volts, and most preferably less than about1 or less than about 0.5 volts. The voltage can be the output of anyconvenient voltage source (e.g. output of an integrated circuit, powersupply, logic gate, potentiostat, microprocessor (CPU), etc.) that canprovide a voltage/signal for writing, reading, or refreshing the storagecell(s).

The method can further involve detecting the oxidation state of thestorage medium and thereby reading out the data stored therein. Thedetection (read) can optionally involve refreshing the oxidation stateof the storage medium. The read (detecting) can involve analyzing areadout signal in the time or frequency domain and can thus involveperforming a Fourier transform on the readout signal. The detection canbe by any of a variety of methods including, but not limited to avoltammetric method.

This invention additionally provides the memory devices of thisinvention (e.g. memory cells) in a computer system. In addition computersystems utilizing the memory devices of this invention are provided.Preferred computer systems include a central processing unit, a display,a selector device, and a memory device comprising the storage devices(e.g. storage cells) of this invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a basic molecular memory unit “storage cell” of thepresent invention.

FIG. 2 illustrates the disposition of the storage cell(s) of theinvention on a chip.

FIG. 3 illustrates a preferred chip-based embodiment of this invention.A two-level chip is illustrated showing working electrodes 101,orthogonal reference electrodes 103, and storage elements 102.

FIG. 4 illustrates the three-dimensional architecture of a single memorystorage cell (memory element) on the chip.

FIG. 5 shows examples of double-decker sandwich coordination compoundarchitectures.

FIG. 6 shows examples of triple-decker sandwich coordination compoundarchitectures.

FIG. 7A shows triple-decker sandwich compounds for attachment to anelectroactive surface with a thiol linker, with vertical arrangment ofthe macrocycles with respect to the surface.

FIG. 7B shows triple-decker sandwich compounds for attachment to anelectroactive surface with a thiol linker, with horizontal arrangment ofthe macrocycles with respect to the surface.

FIG. 8 illustrates two triple decker coordination compounds, whoseoxidation potentials are shown in Table 1.

FIG. 9 shows the triple decker compounds of FIG. 8 derivatized forattachment to an electroactivc surface with a thiol linker.

FIG. 10 shows covalently linked triple-decker sandwich molecules thatare useful for accessing multiple oxidation states.

FIG. 11 shows the achievement of a vertical orientation on anelectroactive surface with only one of the two triple deckers directlyattached thereto.

FIG. 12 shows a sandwich molecule in which one porphyrin bears fourdifferent meso-substituents.

FIG. 13 displays a related sandwich compound architecture that employs a(Por)Eu(Pc)Eu(Por) triple decker rather than a (Por)Eu(Pc)Eu(Pc)architecture used in FIG. 12.

FIG. 14 shows a sandwich compound that incorporates two triple-deckersandwich molecules and two ferrocenes.

FIG. 15 illustrates writing to a molecular memory molecule of thisinvention. In preferred embodiments, this is accomplished through theapplication of very short (e.g., microsecond) pulses applied at avoltage sufficient to oxidize a storage medium (e.g., a sandwichcoordination compound) to the appropriate redox state as summarized inthis figure. Thus, each redox state of the composite multiunitnanostructure (e.g., a sandwich coordination compound array) can beaccessed. This can be accomplished via the electrochemical oxidation ofthe molecule in stepwise increments.

FIG. 16 illustrates a sinusoidal voltammetry system suitable for readoutof the memory devices of this invention.

FIG. 17 illustrates a computer system embodying the memory devicesdescribed herein. Typically the memory device will be fabricated as asealed “chip”. Ancillary circuitry on the chip and/or in the computerpermits writing bits into the memory and retrieving the writteninformation as desired.

FIG. 18 illustrates the memory devices of this system integrated into astandard computer architecture or computer system 200.

FIG. 19 illustrates the porphyrin building blocks used to preparecorresponding triple decker building blocks.

FIG. 20 illustrates the product mixture containing these triple deckersas well as traces of two double deckers, produced by the treatment of(Por)Eu(acac) with Li₂Pc.

FIG. 21 illustrates building block triple-decker complexes of generalstructure (Pc)Eu(Pc)Eu(Por).

FIG. 22 illustrates the coupling of the iodo-substituted triple decker(Pc)Eu(Pc)Eu(IPT-Por) and 4-ethynyl-1-(S-acetylthio)benzene underPd-mediated coupling conditions (Pd(PPh₃)₂Cl₂, CuI) in the presence ofthe base N,N-diisopropylethylamine.

FIG. 23 illustrates the coupling of the ethynyl-substituted tripledecker (Pc)Eu(Pc)Eu(EB-Por) and 4-iodo-1-(S-acetylthio)benzene under thePd-coupling conditions (Pd₂(dba)₃, tri-o-tolylphosphine) used forjoining porphyrin building blocks.

FIG. 24A illustrates the production of the desired ethyne-linked dyad(Dyad 1) along with a butadiyne-linked dyad by treatment oftriple-decker (Pc)Eu(Pc)Eu(IET-Por) with (Pc)Eu(Pc)Eu(E′T-Por) underPd-mediated coupling conditions (Pd(PPh₃)₂Cl₂, CuI).

FIG. 24B illustrates the selective production of the desiredethyne-linked dyad (Dyad 1) by treatment of triple-decker(Pc)Eu(Pc)Eu(IET-Por) with (Pc)Eu(Pc)Eu(E′T-Por) under Pd-mediatedcoupling conditions (Pd₂(dba)₃ and P(o-tolyl)₃ in the absence of copperreagents).

FIG. 25 illustrates the selective production of the desiredbutadiyne-linked dyad (Dyad 2) by treatment of triple-decker(Pc)Eu(Pc)Eu(E′T-Por) under Pd-mediated Glaser coupling conditions(Pd(PPh₃)₂Cl₂, CuI₂).

FIG. 26 illustrates the synthesis of triple decker complexes using thevarious porphyrin and phthalocyanine components.

FIG. 27 illustrates the retrosynthetic analysis of twoS-(acetylthio)-derivatized triple deckers of general structure(Pc)Eu(Pc)Eu(Por).

FIG. 28 illustrates the synthesis of a tripentyl mono-ethynyl porphyrinfor use in preparing the triple decker building blocks.

FIG. 29 illustrates the rational synthesis of a triaryl mono-ethynylporphyrin for use in preparing the triple decker building blocks.

FIG. 30 illustrates deprotection routes for obtaining the porphyinbearing the free ethyne unit.

FIG. 31 illustrates the synthesis of a mono-ethynyl triple deckerbuilding block. Each triple decker exists as a mixture of regioisomersdue to the positions of substitution of the t-butyl groups on thephthalocyanine macrocycles.

FIG. 32 illustrates the synthesis of a triple decker building blockbearing a protected ethyne unit and the subsequent deprotection givingthe free ethyne.

FIG. 33 illustrates the production of the desiredS-(acetylthio)-derivatized triple decker (13) by Pd-mediated coupling aswell as the formation of a by-product (30) derived from an acetyltransfer reaction and the butadiyne-linked dyad (29) derived fromhomo-coupling.

FIG. 34 illustrates the synthesis of an S-(acetylthio)-derivatizedtriple decker via an approach that avoids forming the triple deckerby-product derived from an acetyl transfer reaction.

FIG. 35 illustrates the synthesis of an S-(acetylthio)-derivatizedtriple decker (15) and the production of a by-product (31) derived froman acetyl transfer reaction.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

As noted above, this invention provides novel high density memorydevices that are electrically addressable permitting effective readingand writing, that provide a high memory density (e.g., 10¹⁵ bits/cm³),that provide a high degree of fault tolerance, and that are amenable toefficient chemical synthesis and chip fabrication.

The terms “sandwich coordination compound” or “sandwich coordinationcomplex” refer to a compound of the formula L^(n)M^(n−1), where each Lis a heterocyclic ligand (as described below), each M is a metal, n is 2or more, most preferably 2 or 3, and each metal is positioned between apair of ligands and bonded to one or more hetero atom (and typically aplurality of hetero atoms, e.g., 2, 3, 4, 5) in each ligand (dependingupon the oxidation state of the metal). Thus sandwich coordinationcompounds are not organometallic compounds such as ferrocene, in whichthe metal is bonded to carbon atoms. The ligands in the sandwichcoordination compound are generally arranged in a stacked orientation(i.e., are generally cofacially oriented and axially aligned with oneanother, although they may or may not be rotated about that axis withrespect to one another). See, e.g., D. Ng and J. Jiang, Sandwich-typeheteroleptic phthalocyaninato and porphyrinato metal complexes, ChemicalSociety Reviews 26, 433-442 (1997).

The term “double-decker sandwich coordination compound” refers to asandwich coordination compound as described above where n is 2, thushaving the formula L¹-M¹-L², wherein each of L¹ and L² may be the sameor different. See, e.g., J. Jiang et al., Double-decker Yttrium(III)Complexes with Phthalocyaninato and Porphyrinato Ligands, J. PorphyrinsPhthalocyanines 3, 322-328 (1999).

The term “triple-decker sandwich coordination compound” refers to asandwich coordination compound as described above where n is 3, thushaving the formula L¹-M¹-L²-M²-L³, wherein each of L¹, L² and L³ may bethe same or different, and M¹ and M² may be the same or different. See,e.g., D. Arnold et al., Mixed Phthalocyaninato-PorphyrinatoEuropium(III) Triple-decker Sandwich Complexes Containing a ConjugatedDimeric Porphyrin Ligand, Chemistry Letters 483-484 (1999).

The term “homoleptic sandwich coordination compound” refers to asandwich coordination compound as described above wherein all of theligands L are the same.

The term “heteroleptic sandwich coordination compound” refers to asandwich coordination compound as described above wherein at least oneligand L is different from the other ligands therein.

The term “heterocyclic ligand” as used herein generally refers to anyheterocyclic molecule consisting of carbon atoms containing at leastone, and preferably a plurality of, hetero atoms (e.g., N, O, S, Se,Te), which hetero atoms may be the same or different, and which moleculeis capable of forming a sandwich coordination compound with anotherheterocyclic ligand (which may be the same or different) and a metal.Such heterocyclic ligands are typically macrocycles, particularlytetrapyrrole derivatives such as the phthalocyanines, porphyrins, andporphyrazines. See, e.g., T.-H. Tran-Thi, Assemblies of phthalocyanineswith porphyrins and porphyrazines: ground and excited state opticalproperties, Coordination Chemistry Reviews 160, 53-91 (1997).

The term “oxidation” refers to the loss of one or more electrons in anelement, compound, or chemical substituent/subunit. In an oxidationreaction, electrons are lost by atoms of the element(s) involved in thereaction. The charge on these atoms must then become more positive. Theelectrons are lost from the species undergoing oxidation and soelectrons appear as products in an oxidation reaction. An oxidation istaking place in the reaction Fe²⁺(aq)→Fe³⁺(aq)+e⁻ because electrons arelost from the species being oxidized, Fe²⁺(aq), despite the apparentproduction of electrons as “free” entities in oxidation reactions.Conversely the term reduction refers to the gain of one or moreelectrons by an element, compound, or chemical substituent/subunit.

An “oxidation state” refers to the electrically neutral state or to thestate produced by the gain or loss of electrons to an element, compound,or chemical substituent/subunit. In a preferred embodiment, the term“oxidation state” refers to states including the neutral state and anystate other than a neutral state caused by the gain or loss of electrons(reduction or oxidation).

The term “multiple oxidation states” means more than one oxidationstate. In preferred embodiments, the oxidation states may reflect thegain of electrons (reduction) or the loss of electrons (oxidation).

The term “different and distinguishable” when referring to two or moreoxidation states means that the net charge on the entity (atom,molecule, aggregate, subunit, etc.) can exist in two different states.The states are said to be “distinguishable” when the difference betweenthe states is greater than thermal energy at room temperature (e.g. 0°C. to about 40° C.).

The term “electrode” refers to any medium capable of transporting charge(e.g. electrons) to and/or from a storage molecule. Preferred electrodesare metals or conductive organic molecules. The electrodes can bemanufactured to virtually any 2-dimensional or 3-dimensional shape (e.g.discrete lines, pads, planes, spheres, cylinders, etc.).

The term “fixed electrode” is intended to reflect the fact that theelectrode is essentially stable and unmovable with respect to thestorage medium. That is, the electrode and storage medium are arrangedin an essentially fixed geometric relationship with each other. It is ofcourse recognized that the relationship alters somewhat due to expansionand contraction of the medium with thermal changes or due to changes inconformation of the molecules comprising the electrode and/or thestorage medium. Nevertheless, the overall spatial arrangement remainsessentially invariant. In a preferred embodiment this term is intendedto exclude systems in which the electrode is a movable “probe” (e.g. awriting or recording “head”, an atomic force microscope (AFM) tip, ascanning tunneling microscope (STM) tip, etc.).

The term “working electrode” is used to refer to one or more electrodesthat are used to set or read the state of a storage medium and/orstorage molecule.

The term “reference electrode” is used to refer to one or moreelectrodes that provide a reference (e.g. a particular referencevoltage) for measurements recorded from the working electrode. Inpreferred embodiments, the reference electrodes in a memory device ofthis invention are at the same potential although in some embodimentsthis need not be the case.

The term “electrically coupled” when used with reference to a storagemolecule and/or storage medium and electrode refers to an associationbetween that storage medium or molecule and the electrode such thatelectrons move from the storage medium/molecule to the electrode or fromthe electrode to the storage medium/molecule and thereby alter theoxidation state of the storage medium/molecule. Electrical coupling caninclude direct covalent linkage between the storage medium/molecule andthe electrode, indirect covalent coupling (e.g. via a linker), direct orindirect ionic bonding between the storage medium/molecule and theelectrode, or other bonding (e.g. hydrophobic bonding). In addition, noactual bonding may be required and the storage medium/molecule maysimply be contacted with the electrode surface. There also need notnecessarily be any contact between the electrode and the storagemedium/molecule where the electrode is sufficiently close to the storagemedium/molecule to permit electron tunneling between the medium/moleculeand the electrode.

The term “redox-active unit” or “redox-active subunit” refers to amolecule or component of a molecule that is capable of being oxidized orreduced by the application of a suitable voltage.

The term “subunit”, as used herein, refers to a redox-active componentof a molecule.

The terms “storage molecule” or “memory molecule” refer to a moleculehaving one or more oxidation states that can be used for the storage ofinformation (e.g. a molecule comprising one or more redox-activesubunits). Preferred storage molecules have two or more different anddistinguishable non-neutral oxidation states. In addition to thepolymers of Formula I and Formula II herein, a wide variety ofadditional molecules can be used as storage molecules and hence furthercomprise the storage medium. Preferred molecules include, but are notlimited to a porphyrinic macrocycle, a metallocene, a linear polyene, acyclic polyene, a heteroatom-substituted linear polyene, aheteroatom-substituted cyclic polyene, a tetrathiafulvalene, atetraselenafulvalene, a metal coordination complex, abuckminsterfullerene (i.e., a “buckyball”), a triarylamine, a1,4-phenylenediamine, a xanthene, a flavin, a phenazine, aphenothiazine, an acridine, a quinoline, a 2,2′-bipyridyl, a4,4′-bipyridyl, a tetrathiotetracene, and a peri-bridged naphthalenedichalcogenide. Even more preferred molecules include a porphyrin, anexpanded porphyrin, a contracted porphyrin, a ferrocene, a linearporphyrin polymer, and porphyrin array. Certain particularly preferredstorage molecules include a porphyrinic macrocycle substituted at aβ-position or at a meso-position. Molecules well suited for use asstorage molecules include the molecules described herein.

The term “storage medium” refers to a composition comprising a storagemolecule of the invention, preferably bonded to a substrate.

The term “electrochemical cell” consists minimally of a referenceelectrode, a working electrode, a redox-active medium (e.g. a storagemedium), and, if necessary, some means (e.g., a dielectric) forproviding electrical conductivity between the electrodes and/or betweenthe electrodes and the medium. In some embodiments, the dielectric is acomponent of the storage medium.

The terms “memory element”, “memory cell”, or “storage cell” refer to anelectrochemical cell that can be used for the storage of information.Preferred “storage cells” are discrete regions of storage mediumaddressed by at least one and preferably by two electrodes (e.g. aworking electrode and a reference electrode). The storage cells can beindividually addressed (e.g. a unique electrode is associated with eachmemory element) or, particularly where the oxidation states of differentmemory elements are distinguishable, multiple memory elements can beaddressed by a single electrode. The memory element can optionallyinclude a dielectric (e.g. a dielectric impregnated with counterions).

The term “storage location” refers to a discrete domain or area in whicha storage medium is disposed. When addressed with one or moreelectrodes, the storage location may form a storage cell. However if twostorage locations contain the same storage media so that they haveessentially the same oxidation states, and both storage locations arecommonly addressed, they may form one functional storage cell.

Addressing a particular element refers to associating (e.g.,electrically coupling) that memory element with an electrode such thatthe electrode can be used to specifically determine the oxidationstate(s) of that memory element.

The term “storage density” refers to the number of bits per volumeand/or bits per molecule that can be stored. When the storage medium issaid to have a storage density greater than one bit per molecule, thisrefers to the fact that a storage medium preferably comprises moleculeswherein a single molecule is capable of storing at least one bit ofinformation.

The terms “read”, “detect” or “interrogate” interchangeably refer to thedetermination of the oxidation state(s) of one or more molecules (e.g.molecules comprising a storage medium).

The term “refresh” when used in reference to a storage molecule or to astorage medium refers to the application of a voltage to the storagemolecule or storage medium to re-set the oxidation state of that storagemolecule or storage medium to a predetermined state (e.g. the oxidationstate the storage molecule or storage medium was in immediately prior toa read).

The term “E_(1/2)” refers to the practical definition of the formalpotential (B^(o)) of a redox process as defined byB−B^(o)+(RT/nF)ln(D_(ox)/D_(red)) where R is the gas constant, T istemperature in K (Kelvin), n is the number of electrons involved in theprocess, F is the Faraday constant (96,485 Coulomb/mole), D_(ox) is thediffusion coefficient of the oxidized species and D_(red) is thediffusion coefficient of the reduced species.

A voltage source is any source (e.g. molecule, device, circuit, etc.)capable of applying a voltage to a target (e.g. an electrode).

The term “present on a single plane”, when used in reference to a memorydevice of this invention refers to the fact that the component(s) (e.g.storage medium, electrode(s), etc.) in question are present on the samephysical plane in the device (e.g. are present on a single lamina).Components that are on the same plane can typically be fabricated at thesame time, e.g., in a single operation. Thus, for example, all of theelectrodes on a single plane can typically be applied in a single (e.g.,sputtering) step (assuming they are all of the same material).

The phrase “output of an integrated circuit” refers to a voltage orsignal produced by one or more integrated circuit(s) and/or one or morecomponents of an integrated circuit.

A “voltammetric device” is a device capable of measuring the currentproduced in an electrochemical cell as a result of the application of avoltage or change in voltage.

An “amperometric device” is a device capable of measuring the currentproduced in an electrochemical cell as a result of the application of aspecific field potential (“voltage”).

A potentiometric device is a device capable of measuring potentialacross an interface that results from a difference in the equilibriumconcentrations of redox molecules in an electrochemical cell.

A “coulometric device” is a device capable of measuring the net chargeproduced during the application of a potential field (“voltage”) to anelectrochemical cell.

A “sinusoidal voltammeter” is a voltammetric device capable ofdetermining the frequency domain properties of an electrochemical cell.

The term “porphyrinic macrocycle” refers to a porphyrin or porphyrinderivative. Such derivatives include porphyrins with extra ringsortho-fused, or ortho-perifused, to the porphyrin nucleus, porphyrinshaving a replacement of one or more carbon atoms of the porphyrin ringby an atom of another element (skeletal replacement), derivatives havinga replacement of a nitrogen atom of the porphyrin ring by an atom ofanother element (skeletal replacement of nitrogen), derivatives havingsubstituents other than hydrogen located at the peripheral (meso-, β-)or core atoms of the porphyrin, derivatives with saturation of one ormore bonds of the porphyrin (hydroporphyrins, e.g., chlorins,bacteriochlorins, isobacteriochlorins, decahydroporphyrins, corphins,pyrrocorphins, etc.), derivatives obtained by coordination of one ormore metals to one or more porphyrin atoms (metalloporphyrins),derivatives having one or more atoms, including pyrrolic andpyrromethenyl units, inserted in the porphyrin ring (expandedporphyrins), derivatives having one or more groups removed from theporphyrin ring (contracted porphyrins, e.g., corrin, corrole) andcombinations of the foregoing derivatives (e.g. phthalocyanines,porphyrazines, naphthalocyanines, subphthalocyanines, and porphyrinisomers). Preferred porphyrinic macrocycles comprise at least one5-membered ring.

The term porphyrin refers to a cyclic structure typically composed offour pyrrole rings together with four nitrogen atoms and two replaceablehydrogens for which various metal atoms can readily be substituted. Atypical porphyrin is hemin.

The term “multiporphyrin array” refers to a discrete number of two ormore covalently-linked porphyrinic macrocycles. The multiporphyrinarrays can be linear, cyclic, or branched.

A linker is a molecule used to couple two different molecules, twosubunits of a molecule, or a molecule to a substrate. When all arecovalently linked, they form units of a single molecule.

A substrate is a, preferably solid, material suitable for the attachmentof one or more molecules. Substrates can be formed of materialsincluding, but not limited to glass, plastic, silicon, minerals (e.g.quartz), semiconducting materials, ceramics, metals, etc.

The term “aryl” refers to a compound whose molecules have the ringstructure characteristic of benzene, naphthalene, phenanthrene,anthracene, etc. (i.e., either the 6-carbon ring of benzene or thecondensed 6-carbon rings of the other aromatic derivatives). Forexample, an aryl group may be phenyl (C₆H₅) or naphthyl (C₁₀H₇). It isrecognized that the aryl, while acting as substituent can itself haveadditional substituents (e.g. the substituents provided for S^(n) in thevarious formulas herein).

The term “alkyl” refers to a paraffinic hydrocarbon group which may bederived from an alkane by dropping one hydrogen from the formula.Examples are methyl (CH₃—), ethyl (C₂H₅—), propyl (CH₃CH₂CH₂—),isopropyl ((CH₃)₂CH—).

The term “halogen” refers to one of the electronegative elements ofgroup VIIA of the periodic table (fluorine, chlorine, bromine, iodine,astatine).

The term “nitro” refers to an —NO₂ group.

The term “amino” refers to an —NH₂ group.

The term “perfluoroalkyl” refers to an alkyl group where every hydrogenatom is replaced with a fluorine atom.

The term “perfluoroaryl” refers to an aryl group where every hydrogenatom is replaced with a fluorine atom.

The term “pyridyl” refers to an aryl group where one CR unit is replacedwith a nitrogen atom.

The term “cyano” refers to an —CN group.

The term “thiocyanato” refers to an —SCN group.

The term “sulfoxyl” refers to a group of composition RS(O)— where R issome alkyl, aryl, cycloalkyl, perfluoroalkyl, or perfluoroaryl group.Examples include, but are not limited to methylsulfoxyl, phenylsulfoxyl,etc.

The term “sulfonyl” refers to a group of composition RSO₂— where R issome alkyl, aryl, cycloalkyl, perfluoroalkyl, or perfluoroaryl group.Examples include, but are not limited to methylsulfonyl, phenylsulfonyl,p-toluenesulfonyl, etc.

The term “carbamoyl” refers to the group of composition R¹(R²)NC(O)—where R¹ and R² are H or some alkyl, aryl, cycloalkyl, perfluoroalkyl,or perfluoroaryl group. Examples include, but are not limited toN-ethylcarbamoyl, N,N-dimethylcarbamoyl, etc.

The term “amido” refers to the group of composition R¹CON(R²)— where R¹and R² are H or some alkyl, aryl, cycloalkyl, perfluoroalkyl, orperfluoroaryl group. Examples include, but are not limited to acetamido,N-ethylbenzamido, etc.

The term “acyl” refers to an organic acid group in which the —OH of thecarboxyl group is replaced by some other substituent (RCO—). Examplesinclude, but are not limited to acetyl, benzoyl, etc.

In preferred embodiments, when a metal is designated by “M” or “M^(n)”,where n is an integer, it is recognized that the metal may be associatedwith a counterion.

The term “substituent” as used in the formulas herein, particularlydesignated by S or S^(n) where n is an integer, in a preferredembodiment refer to redox-active groups (subunits) that can be used toadjust the redox potential(s) of the subject compound. Preferredsubstituents include, but are not limited to, aryl, phenyl, cycloalkyl,alkyl, halogen, alkoxy, alkylthio, perfluoroalkyl, perfluoroaryl,pyridyl, cyano, thiocyanato, nitro, amino, alkylamino, acyl, sulfoxyl,sulfonyl, amido, and carbamoyl. In preferred embodiments, a substitutedaryl group is attached to a porphyrin or a porphyrinic macrocycle, andthe substituents on the aryl group are selected from the groupconsisting of aryl, phenyl, cycloalkyl, alkyl, halogen, alkoxy,alkylthio, perfluoroalkyl, perfluoroaryl, pyridyl, cyano, thiocyanato,nitro, amino, alkylamino, acyl, sulfoxyl, sulfonyl, amido, andcarbamoyl. Additional substituents include, but are not limited to,4-chlorophenyl, 4-trifluoromethylphenyl, and 4-methoxyphenyl. Preferredsubstituents provide a redox potential range of less than about 5 volts,preferably less than about 2 volts, more preferably less than about 1volt.

The phrase “provide a redox potential range of less than about X volts”refers to the fact that when a substituent providing such a redoxpotential range is incorporated into a compound, the compound into whichit is incorporated has an oxidation potential less than or equal to Xvolts, where X is a numeric value.

One embodiment of this invention is illustrated in FIG. 1. The basicmemory device, a “storage cell” 100 comprises a working electrode 101electrically coupled to a storage medium 102 comprising a multiplicityof storage molecules 105. The storage cell optionally includes anelectrolyte 107 and a reference electrode 103. The storage medium has amultiplicity of different and distinguishable oxidation states,preferably a multiplicity of different and distinguishable non-neutraloxidation states, and can change oxidation (charge) state when a voltageor signal is applied thereby adding or removing one or more electrons.Each oxidation state may be used to represent stored information.

The storage medium may remain in the set oxidation state until anothervoltage is applied to alter that oxidation state, can be refreshed, orthe information content can be allowed to dissipate over time. Theoxidation state of the storage medium can be readily determined using awide variety of electronic (e.g. amperometric, coulometric,voltammetric) methods thereby providing rapid readout.

The storage medium comprises molecules having a single oxidation stateand/or molecules having multiple different and distinguishablenon-neutral oxidation states. Thus, for example, in one embodiment, thestorage medium can comprise eight different species of storage moleculeseach having one non-neutral oxidation state and thereby store threebits, or one byte if the oxidation states are independently accessed. Inanother embodiment, the storage medium can comprise one species ofmolecule that has eight different and distinguishable oxidation statesand likewise store three bits or one byte in that manner as well. Asexplained herein, a large number of different molecules having differentnumbers of oxidation states can be used for the storage medium.

Because molecular dimensions are so small (on the order of angstroms)and individual molecules in the devices of this invention can storemultiple bits, the storage devices of this invention therefore offerremarkably high storage densities (e.g. >10¹⁵ bits/cm³).

Moreover, unlike prior art, the devices of this invention are capable ofa degree of self-assembly and hence easily fabricated. Because thedevices are electrically (rather than optically) addressed, and becausethe devices utilize relatively simple and highly stable storageelements, they are readily fabricated utilizing existing technologiesand easily incorporated into electronic devices. Thus, the molecularmemory devices of this invention have a number of highly desirablefeatures.

Because the storage medium of the devices described herein iselectrically-addressed, the devices are amenable to the construction ofa multilayered chip architecture. An architecture compatible with such athree-dimensional structure is essential to achieve the objective of10¹⁵ bits/cm³. In addition, because writing and reading is accomplishedelectrically, many of the fundamental problems inherent with photonicsare avoided. Moreover, electrical reading and writing is compatible withexisting computer technology for memory storage.

In addition, the devices of this invention achieve a high level ofdefect tolerance. Defect tolerance is accomplished through the use ofclusters of molecules (up to several million in a memory cell). Thus,the failure of one or a few molecules will not alter the ability to reador write to a given memory cell that constitutes a particular bit ofmemory. In preferred embodiments, the basis for memory storage relies onthe oxidation state(s) of porphyrins or other porphyrinic macrocycles ofdefined energy levels. Porphyrins and porphyrinic macrocycles are wellknown to form stable radical cations. Indeed, the oxidation andreduction of porphyrins provide the foundation for the biologicalprocesses of photosynthesis and respiration. Porphyrin radical cationscan be formed chemically on the benchtop exposed to air. Double andtriple decker sandwich molecules comprises of porphyrinic ligandsexhibit essentially the same phenomena.

Preferred storage molecules of this invention molecule can hold multipleholes, corresponding to multiple bits. In contrast, the dyes(photochromic, electrochromic, redox) and molecular machines areinvariably bistable elements. Bistable elements exist either in ahigh/low state and hence can only store a single bit.

Reading can be accomplished non-destructively or destructively asrequired in different chip applications. The speed of reading isconservatively estimated to lie in the MHz to GHz range. Oxidation ofthe porphyrins or other porphyrinic macrocycles can be achieved atrelatively low potential (and at predesignated potentials throughsynthetic design), enabling memory storage to be achieved at very lowpower. Porphyrins and porphyrin radical cations are stable across abroad range of temperatures, enabling chip applications at lowtemperature, room temperature, or at elevated temperatures. Double andtriple decker sandwich molecules comprised of porphyrinic ligandsexhibit essentially the same phenomena.

Fabrication of the devices of this invention relies on known technology.The synthesis of the storage media takes advantage of establishedbuilding block approaches in porphyrin and other porphyrinic macrocyclechemistry. Synthetic routes have been developed to make the porphyrinand porphyrinic macrocycle building blocks, to join them in covalentnanostructures, and to purify them to a high level (>99%).

In preferred embodiments, the storage medium nanostructures are designedfor directed self-assembly on gold surfaces. Such self-assemblyprocesses are robust, result in the culling out of defective molecules,and yield long-range order in the surface-assembled cluster.

Porphyrin-thiols have been assembled on electroactive surfaces. Thearrays that define the addressable bits of memory can be achievedthrough conventional microfabrication techniques. The storage moleculesare self-assembled onto these electrode arrays and attached to the goldsurface using conventional dipping methods.

I. Uses of the Storage Device

One of ordinary skill in the art will appreciate that the memory devicesof this invention have wide applicability in specialized andgeneral-purpose computer systems. Of course commercial realization ofthe device(s) will be facilitated by the adoption of computerarchitecture standards compatible with this technology. In addition,commercial adoption of this technology will be facilitated by the use ofother molecular electronic components that will serve as on-chip buffersand decoders (that is, molecular logic gates), and the like. Inaddition, commercialization will be facilitated by the development of afull manufacturing infrastructure.

Regardless, prior to the development of a fully integrated design andmanufacturing platform for molecular electronic information storage andtransfer, even early generation prototype molecular memory devicesdescribed herein have utility in a variety of personal or industrialapplications. For example, a prototype 1024/512-bit molecular memorydevice has sufficient capacity to hold a substantial base of personaland/or other proprietary information. This information could betransported anywhere in the world virtually undetected owing to theextremely small size of the device. If detected, the memory device iseasily erased simply by applying a low potential reverse bias currentacross all memory cells. This protection mechanism can be readilyincorporated into any type of transport architecture designed for thememory device.

Among other things, the memory devices of this invention have sufficientcapacity to hold information that could be used in a wide assortment ofpersonal digital assistants or “smart cards”. Even a memory device thatdegrades upon multiple read cycles is extremely useful if the number ofread cycles is highly limited (perhaps only one). A memory device thatdegrades upon multiple read cycles or simply with time is also useful inapplications where long-term data persistence is not needed. Thus,numerous applications for early generation memory devices presentthemselves. Successes of the memory devices in these applications willfoster even more rapid full-scale commercialization of the technology.

II. Architecture of the Storage Device

The basic storage cell (electrode(s) and storage medium) of thisinvention can be incorporated into a functional device in a wide varietyof configurations. One chip-based embodiment of this invention isillustrated in FIG. 2. As illustrated in FIG. 2 the storage medium 102is disposed in a number of storage locations 104. Each storage locationis addressed by a working electrode 101 and a reference electrode 103 sothat the storage medium 102 combined with the electrodes forms a storagecell 100 at each storage location.

One particularly preferred chip-based embodiment is illustrated in FIG.3. In the illustrated embodiment, a plurality of working electrodes 101and reference electrodes 103 are illustrated each addressing storagemedia 102 localized at discrete storage locations thereby forming aplurality of storage cells 100. Multiple storage cells can be associatedwith a single addressing electrode as long as oxidation states of thestorage cells are distinguishable from each other. It should be notedthat this forms a functional definition of a storage cell. Where twodiscrete areas of storage medium are addressed by the same electrode(s)if the storage media comprise the same species of storage molecule thetwo discrete areas will functionally perform as a single storage cell,i.e. the oxidation states of both locations will be commonly set, and/orread, and/or reset. The added storage location, however, will increasethe fault tolerance of the storage cell as the functional storage cellwill contain more storage molecules. In another embodiment, eachindividual storage cell is associated with a single addressingelectrode.

In preferred embodiments, the storage medium comprising the storagecells of a memory device is electrically coupled to one or morereference electrodes. The reference electrode(s) can be provided asdiscrete electrodes or as a common backplane.

The chip illustrated in FIG. 3 has two levels of working electrodes andhence two levels of storage cells 100 (with numerous storage cells oneach level). Of course, the chip can be fabricated with a single levelof electrodes and memory element or literally hundreds or thousands ofdifferent levels of storage cell(s), the thickness of the chip beinglimited essentially by practical packaging and reliability constraints.

In particularly preferred embodiments, a layer of dielectric materialoptionally imbedded with counterions to ensure electrical connectivitybetween the working and reference electrode(s) and stability of thecationic species in the absence of applied potential (latching) isdisposed in the storage cell. In some embodiments, the dielectricmaterial can be incorporated into the storage medium itself.

While, in some preferred embodiments, feature sizes are rather large(e.g. memory elements approximately (10×10×10 μm) and electrodethickness ˜200 nm, feature size can be reduced at will so that featuresizes are comparable to those in conventional silicon-based devices(e.g., 50 nm-100 nm on each axis).

In a preferred embodiment, the storage device includes: (1) A goldworking electrode (e.g., 200 nm thick), deposited on a nonconductingbase, and line-etched to achieve electrode widths of 10's to 100's ofnm. (2) A monolayer of self-assembled nanostructures (storage molecules105) attached to the gold surface via the sulfur atom of thep-thiophenyl group. (3) A 100-nm thick layer of dielectric material 107embedded with counterions to ensure electrical connectivity to thereference electrode and stability of the cationic species in the absenceof applied potential (latching). (4) A 200-nm thick nonpolarizablereference electrode 103 line-etched in the same fashion as those of theworking electrode 101, but assembled with lines orthogonal to the latterelectrode. (5) A mirror image construct that utilizes the same referenceelectrode. Thus, in one embodiment, the three-dimensional architectureof a single memory storage location (memory element) on the chip willlook as indicated in FIG. 4.

While the discussion herein of electrodes is with respect to goldelectrodes, it will be recognized that numerous other materials will besuitable. Thus, electrode materials include, but are not limited togold, silver, copper, other metals, metal alloys, organic conductors(e.g. doped polyacetylene, doped polythiophene, etc.), nanostructures,crystals, etc.

Similarly, the substrates used in the fabrication of devices of thisinvention include, but are not limited to glasses, silicon, minerals(e.g. quartz), plastics, ceramics, membranes, gels, aerogels, and thelike.

III. Fabrication and Characterization of the Storage Device

A. Fabrication.

The memory devices of this invention can be fabricated using standardmethods well known to those of skill in the art. In a preferredembodiment, the electrode layer(s) are applied to a suitable substrate(e.g. silica, glass, plastic, ceramic, etc.) according to standard wellknown methods (see, e.g., Rai-Choudhury (1997) The Handbook ofMicrolithography, Micromachining, and Microfabrication, SPIE OpticalEngineering Press; Bard & Faulkner (1997) Fundamentals ofMicrofabrication). In addition, examples of the use of micromachiningtechniques on silicon or borosilicate glass chips can be found in U.S.Pat. Nos. 5,194,133, 5,132,012, 4,908,112, and 4,891,120.

In one preferred embodiment a metal layer is beam sputtered onto thesubstrate (e.g., a 10 nm thick chromium adhesion layer is sputtered downfollowed by a 200 nm thick layer of gold). Then maskless laser ablationlithography (see below, performed e.g., with a Nd:YAG laser, is used tocreate features with micron dimensions, or with an excimer laser tocreate features of nanometer dimensions) will create an array ofparallel lines of conductor (e.g., gold), used as the working electrodeswith dimensions ranging between a few microns to tens of nanometers.

Once the electrode array is formed, the entire array, or portions of thearray, or individual electrodes are wetted (e.g. immersed or spotted)with one or more solutions of the appropriate derivatized storage media(e.g. thiol-substituted porphyrin nanostructures), and the constituentsof the memory medium (e.g., monomeric porphyrin subunits) self-assembleon the micro-sized gold arrays to form the memory elements. It will beappreciated that different solutions can be applied to different regionsof the electrode array to produce storage cells comprising differentstorage media. Methods of spotting different reagents on surfaces (e.g.on glass surfaces) at densities up to tens of thousands of differentspecies/spots per cm² are known (see, e.g., U.S. Pat. No: 5,807,522).

Then a suitable electrolyte layer (e.g. a thin layer of Nafion® polymer)approximately 1 nm to 1000 nm, preferably about 100 nm to about 500 nm,more preferably about 10 nm to about 100 nm and most preferably aboutone hundred nanometers thick) will be cast over the entire surface ofthe chip. This polymer serves to hold the electrolyte forelectrochemical reaction. Finally, the entire chip is coated with alayer (e.g., 10 nm to about 1000 nm, more preferably 100 nm to about 300nm and most preferably about 200 nm of conducting material (e.g. silver)which acts as a reference electrode 103.

The chip is then turned 90 degrees, and maskless laser ablationlithography will be performed again to create a second array of parallellines that are perpendicular to the original set. This forms a threedimensional array of individual memory elements, where each element isformed by the intersection of these two perpendicular linear arrays (seeFIG. 4).

Each individual element can be addressed by selecting the appropriate Xand Y logic elements, corresponding to one gold working electrode andone reference electrode separated by the Nafion® polymer/electrolytelayer. Since this structure is inherently three dimensional, it shouldbe possible to extend the array into the Z-direction, creating a 3-Darray of memory elements as large as it is feasible to connect to.

These structures are initially created on the micron scale. It ispossible to decrease the size of these structures to sub-microndimensions. It is possible to create these structures on a scale similarto silicon microstructures created with conventional nanolithographictechniques (i.e. 100-200 nm). This would allow the interfacing of thememory elements with conventional silicon-based semiconductorelectronics.

In the laser-ablation lithography discussed above, coherent light issent through a beam splitter (50% transmittance) and reflected by amirror to make two nearly parallel identical beams (Rosenwald et al.(1998) Anal. Chem., 70: 1133-1140). These beams are sent through e.g., a50 cm focal length lens for ease in focusing to a common point. Theplacement of the beams is fine-tuned to allow complete overlap of themode structure of the laser spot. Higher order interference patterns areminimized through the use of high quality optics (1/10 wave surfaceflatness). This ensures that the variation between intensity maxima andminima in the first order will be several orders of magnitude largerthan those formed with second and higher orders. This produces awell-defined pattern of lines across the electrode surface, where thespacing between points of positive interference (D) can be approximatedby the Bragg Equation: nλ=2D sin(θ/2), where λ=wavelength, θ=anglebetween the beams, and n is order. For example, when a Nd:YAG is used at1064 nm, the recombination of the two beams in this manner generates aninterference pattern with ˜2 micron spacing when the angle between the 2beams is 15°. The interference pattern spacing can easily be changed bymodifying the angle between the beams. Attenuation of the beam wasaccomplished by inserting one or more neutral density filters before thebeam splitter. In this way, the exposure of the gold layer to the Nd-YAGinterference pattern can be performed at different beam attenuations toproduce power densities between 1 and 100 MW/cm².

B. Electrically Coupling Storage Medium to Electrode.

In the storage devices of this invention, the storage medium iselectrically coupled to one or more electrodes. The term “electricalcoupling” is used to refer to coupling schemes that permit the storagemedium to gain or lose electrons to the electrode. The coupling can be adirect attachment of the storage medium to the electrode, or an indirectattachment (e.g. via a linker). The attachment can be a covalentlinkage, an ionic linkage, a linkage driven by hydrogen bonding or caninvolve no actual chemical attachment, but simply a juxtaposition of theelectrode to the storage medium. In some embodiments, the electrode canbe some distance (e.g. about 5 Å to about 50 Å) from the storage mediumand electrical coupling can be via electron tunneling.

In some preferred embodiments, a “linker” is used to attach themolecule(s) of the storage medium to the electrode. The linker can beelectrically conductive or it can be short enough that electrons canpass directly or indirectly between the electrode and a molecule of thestorage medium.

The manner of linking a wide variety of compounds to various surfaces iswell known and is amply illustrated in the literature. Means of couplingthe molecules comprising the storage medium will be recognized by thoseof skill in the art. The linkage of the storage medium to a surface canbe covalent, or by ionic or other non-covalent interactions. The surfaceand/or the molecule(s) may be specifically derivatized to provideconvenient linking groups (e.g. thiol, hydroxyl, amino, etc.). Thelinker can be provided as a component of the storage medium molecule(s)or separately. Linkers, when not joined to the molecules to be linkedare often either hetero- or homo-bifunctional molecules that contain twoor more reactive sites that may each form a covalent bond with therespective binding partner (i.e. surface or storage medium molecule).When provided as a component of a storage molecule, or attached to asubstrate surface, the linkers are preferably spacers having one or morereactive sites suitable for bonding to the respective surface ormolecule.

Linkers suitable for joining molecules are well known to those of skillin the art and include, but are not limited to any of a variety of,straight or branched chain carbon linkers, heterocyclic linkers, aminoacid or peptide linkers, and the like. Particularly preferred linkersare described in greater detail below.

C. Addressing the Memory Cells.

Addressing of the storage cell(s) in the devices of this invention isrelatively straightforward. In a simple approach a discrete pair ofelectrodes (one working and one reference electrode) can be connected toevery storage cell. Individual reference electrodes, however are notrequired and can be replaced with one or more common referenceelectrodes connected to all or to a subset of all of the storageelements in a particular device. Alternatively, the common referenceelectrodes can be replaced with one or more conductive “backplanes” eachcommunicating to all, or to a subset, of the storage cells in aparticular device.

Where the storage cells contain identical storage media, each storagecell is preferably addressed with a separate working electrode so thatthe storage (oxidation) states of the storage cells can be distinguishedfrom each other. Where the storage cells contain different storage mediasuch that the oxidation states of one storage cell are different anddistinguishable from the oxidation states of another storage cell, thestorage cells are preferably addressed by a common working electrodethereby reducing the number of electrodes in a device.

In one preferred embodiment, the storage devices of this inventioncontain 64, 128, 256, 512, 1024 or more storage locations per layer (64,128, 256, 512, 1024 or more locations in the mirror image architecture)with each location capable of holding a two bit word. Accordingly, apreferred 1024-bit or a preferred 512-bit chip will contain 8 wiringinterconnects on each of the three electrode grids in the 3-dimensionalarchitecture illustrated in FIG. 4.

D. Characterization of the Memory Device.

The performance (e.g. operating characteristics) of the memory devicesof this invention is characterized by any of a wide variety of methods,most preferably by electrochemical methods (amperometry and sinusoidalvoltammetry, see, e.g., Howell et al. (1986) Electroanal. Chem., 209:77-90; Singhal and Kuhr, (1997) Anal. Chem., 69: 1662-1668), opticalspectroscopy (Schick et al. (1989) J. Am. Chem. Soc. 111: 1344-1350),atomic force microscopy, electron microscopy and imaging spectroscopicmethods. Surface-enhanced resonance and Raman spectroscopy are also usedto examine the storage medium on the electrodes.

Among other parameters, characterization of the memory devices (e.g.,memory cells) involves determining the number of storage mediummolecules (e.g., double and triple decker porphyrin arrays) required fordefect-tolerant operation. Defect tolerance includes factors such asreliably depositing the required number of holes to write the desireddigit and accurately detecting the numbers/transfer rates of the holes.

The long-term resistance of electron/holes to charge-recombination inthe solid-phase medium of the device package is also determined. Usingthese parameters, the device architecture can be optimized forcommercial fabrication.

IV. Architecture of the Storage Medium

The storage medium used in the devices of this invention comprises oneor more species of storage molecule. A preferred storage medium ischaracterized by having a multiplicity of oxidation states. Thoseoxidation states are provided by one or more redox-active units. Aredox-active unit refers to a molecule or to a subunit of a moleculethat has one or more discrete oxidation states that can be set byapplication of an appropriate voltage. Thus, for example, in oneembodiment, the storage medium can comprise one species of redox-activemolecule where that molecule has two or more (e.g. 4) different anddistinguishable oxidation states. Where each species of storage moleculehas a single, non-neutral, oxidation state, the storage medium achievesmultiple bit storage by having a plurality of such molecules where eachmolecule has a different and distinguishable oxidation state (e.g. eachspecies of molecule oxidizes at a different and distinguishablepotential). Of course, each species of molecule preferably has aplurality of different and distinguishable oxidation states.

As indicated above, the storage medium can be broken down intoindividual, e.g., spatially segregated, storage locations. Each storageelement can have a storage medium that is the same or different from theother storage elements in the chip and/or system. Where the storageelements are of identical composition, in preferred embodiments, theyare separately addressed so that information in one element can bedistinguished from information in another element. Where the storageelements are of different composition they can be commonly addressed(where the oxidation states of the commonly addressed storage elementsare distinguishable) or they can be individually addressed.

In certain preferred embodiments the storage medium is juxtaposed to adielectric medium to insure electrical connectivity to a referencevoltage (e.g. a reference electrode, a reference backplane, etc.). Inparticularly preferred embodiments, a layer of dielectric material isimbedded with counterions to ensure electrical connectivity to thereference electrode and stability of the cationic species in the absenceof applied potential (latching) disposed between the reference workingelectrode(s).

Dielectric materials suitable for the devices of this invention are wellknown to those of skill in the art Such materials include, but are notlimited to Nafion® polymer, cellulose acetate, polystyrene sulfonate,poly(vinylpyridine), electronically conducting polymers such aspolypyrrole and polyaniline, etc.

The sandwich coordination compounds identified herein are ideally suitedfor molecular based memory storage. These compounds have uniqueelectroactive properties, available modular synthetic chemistry, and inconjunction with thiols, and other linkers described herein, undergodirected self-assembly on electroactive surfaces.

A. Sandwich Coordination Compounds.

Over the past two decades a variety of double-decker and triple-deckersandwich molecules comprised of porphyrinic macrocycles and metals hasbeen created ((J. Jiang et al. Inorg. Chim. Acta 1997, 255, 59-64; D. Nget al., Chem. Soc. Rev. 1997, 26, 433-442; D. Chabach et al., Angew.Chem. Int. Ed. Engl. 1996, 35, 898-899)). The metals are generallycomprised of the lanthanide series and Y, as well as others discussedbelow, which have properties similar to those of the lanthanides. Infact the only lanthanide that has not been incorporated into a porphyrinsandwich complex is the radioactive element Pm. Examples of variousdouble-decker architectures are shown in FIG. 5. The architecturesinclude a bis-phthalocyanine sandwich molecule ((Pc)M(Pc)), abis-porphyrin sandwich molecule ((Por)M(Por)), and a hybridphthalocyanine-porphyrin sandwich molecule ((Pc)M(Por)). It isunderstood that each porphyrinic macrocycle can bear substituents at theperipheral β- or meso-carbon atoms (not shown). In the bis-porphyrinicsandwich molecules, the two macrocycles can be identical (homoleptic) ordifferent (heteroleptic).

Examples of various triple-decker architectures are shown in FIG. 6. Thearchitectures include an all-phthalocyanine sandwich molecule((Pc)M(Pc)M(Pc)), an all-porphyrin sandwich molecule((Por)M(Por)M(Por)), two configurations of two porphyrins and onephthalocyanine ((Por)M(Pc)M(Por), (Pc)M(Por)M(Por)) and twoconfigurations of one porphyrin and two phthalocyanines((Pc)M(Por)M(Pc), (Pc)M(Pc)M(Por)). It is understood that eachporphyrinic macrocycle can bear substituents at the peripheral carbonatoms (not shown). It is also understood that the two metals in thetriple decker can be identical or different (not shown). Heteronuclearheteroleptic or homoleptic complexes can also be prepared (heteronuclearrefers to the use of different metals in the triple decker coordinationcompound).

The triple deckers are attractive for molecular-based informationstorage due to the multiple accessible oxidation states (which in turnare a consequence of the tight coupling of the porphyrinic macrocyclesin the sandwich architectures). The triple deckers generally exhibitfour oxidation potentials in the range −0.2 to 1.4 V (vs. Ag/Ag⁺). (Notethat all potentials denoted here are referenced to, or have been scaledto, the Ag/Ag⁺ electrode for internal consistency. Reported valuesmeasured against the saturated calomel electrode have had 170 mVsubtracted in order to give a value appropriate for the Ag/Ag⁺electrode, based on the use of ferrocene as a standard.) For example,the (Por)Eu(Pc)Eu(Por) triple decker with Ar=4-t-butylphenyl on the fourmeso positions of the porphyrin gave anodic waves at 0.23, 0.62, 0.95,and 1.23 V, corresponding to formation of the monocation, dication,trication, and tetracation, respectively (J. Jiang et al., Inorg. Chim.Acta 1998, 268, 49-53).

Particular examples of sandwich coordination compounds that may be usedto carry out the present invention have the Formula XI (fordouble-decker sandwich compounds) or Formula XII (for triple-deckersandwich compounds):

wherein:

M¹ and M² (when present) are metals independently selected from thegroup consisting of metals of the lanthanide series (Ln=La, Ce, Pr, Nd,Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, as well as Y, Zr, Hf, andBi, and in the actinide series Th and U (radioactive elements such as Pmare generally less preferred);

L¹, L² and L³ (when present) are independently selected ligands (e.g.,porphyrinic macrocycles); and

Q¹, Q² and Q³ may be present or absent and when present areindependently selected linkers as described in section III B above (thelinker preferably including a protected or unprotected reactive groupsuch as thio, seleno or telluro group). Preferably, at least one of Q¹,Q², and Q³ is present.

It will also be appreciated that each ligand L may be substituted with asingle linker Q, or may be multiply substituted with linkers Q, asexplained in greater detail below. Thus the molecule of Formula XI orFormula XII may be covalently linked to an electrode or substrate by atleast one of Q¹, Q², or Q³.

Each ligand L may be further substituted without departing from thescope of the compounds of Formula XI or Formula XII above. For example,and as explained in greater detail below, ligands may be covalentlyjoined to a metallocene group, to another porphyrinic macrocycle, to aligand of another sandwich coordination compound, etc.

Particular embodiments of the compounds of Formula XI and XII above,which provide additional memory storage as discussed in section IV Cbelow, are those represented by Formula XIII and Formula XIV:

wherein:

M¹ and M² are as given above;

L¹, L² and L³ are as given above;

Q¹, Q² and Q³ are as given above; and

P¹, P², and P³ may be present or absent and, when present, represent anindependently selected oxidizable group such as a porphyrinicmacrocycle, a metallocene such as ferrocene, etc. (which may be joinedto the corresponding L^(n) through a linker as described below).

Thus, particular embodiments of Formulas I and II above, and which alsoprovide additional storage capability as discussed in section IV Cbelow, include the case where two sandwich coordination compounds arelinked together, as represented by Formula XV and Formula XVI below:

wherein:

M¹ and M² are as given above and M³ and M⁴ are independently selectedfrom the same group as M¹ and M²;

L¹, L² and L³ are as given above, and L⁴, L⁵, and L⁶ are independentlyselected from the same group as L¹, L², and L³;

Q¹, Q² and Q³ may be present or absent and are as given above, and Q⁴,Q⁵, and Q⁶ may be present or absent and are independently selected fromthe same group as Q¹, Q², and Q³ (subject to the proviso that at leastone of Q¹ through Q⁶ is present); and

J¹, J², and J³ may be present or absent and when present representindependently selected linkers (subject to the proviso that at least oneof J¹, J², or J³ is present). Each linker J^(n) can be a linker of thesame category or structure as described with respect to linker Q¹herein, but is preferably a linear linker.

Compounds of Formula XV and XVI above may be further substituted in themanner described in connection with the compounds of Formulas XIII andXIV above, to provide compounds of Formula XVII and Formula XVIII below(such compounds, particularly those of Formula XVIII, provide anarchitecture that enables the storage of information for counting offrom 0 to 10, as discussed in section IV D below):

wherein:

M¹, M², M³ and M⁴ are as given above;

L¹, L², L³, L⁴, L⁵, and L⁶ are as given above;

Q¹, Q², Q³, Q⁴, Q⁵, and Q⁶ are as given above;

J¹, J², and J³ may be present or absent and when present representindependently selected linkers (subject to the proviso that at least oneof J¹, J², or J³ is present);

P¹, P², and P³ are as given above, and P⁴, P⁵, and P⁶ are independentlyselected from the same group as P¹, P² and P³.

In the compounds of Formula XV and XVII above, L⁵ could further besubstituted or extended with -M⁴-L⁶-Q⁶, or -M⁴-L⁶-Q⁶P⁶, as where adouble decker compound is linked to a triple decker compound.

Particular examples of porphyrinic macrocycles that may be used asligands to carry out the present invention include compounds of theFormula XX and Formula XXI below:

wherein:

K¹, K², K³, K⁴, K⁵, K⁶, K⁷, and K⁸ are independently selected from thegroup consisting of N, O, S, Se, Te, and CH;

S¹, S², S³, S⁴, S⁵, S⁶, S⁷, S⁸, S⁹, S¹⁰, s¹¹, and S¹² are independentlyselected substituents that preferably provide a redox potential of lessthan about 5, 2 or even 1 volt. Example substituents S¹, S², S³, S⁴include, but are not limited to, H, aryl, phenyl, cycloalkyl, alkyl,halogen, alkoxy, alkylthio, perfluoroalkyl, perfluoroaryl, pyridyl,cyano, thiocyanato, nitro, amino, alkylamino, acyl, sulfoxyl, sulfonyl,imido, amido, and carbamoyl.

In addition, each pair of S¹ and S², S³ and S⁴, S⁵ and S⁶, and S⁷ andS⁸, may independently form an annulated arene, such as a benzene,naphthalene, or anthracene, which in turn may be unsubstituted orsubstituted one or more times with a substituent that preferablyprovides a redox potential of less than about 5, 2 or even 1 volt, suchas H, aryl, phenyl, cycloalkyl, alkyl, halogen, alkoxy, alkylthio,perfluoroalkyl, perfluoroaryl, pyridyl, cyano, thiocyanato, nitro,amino, alkylamino, acyl, sulfoxyl, sulfonyl, imido, amido, andcarbamoyl. Examples of such annulated arenes include, but are notlimited to:

(It being understood that the rings are appropriately conjugated toretain aromaticity of the fused rings); and wherein each substituent S′is independently selected and preferably provides a redox potential ofless than about 5, 2 or even 1 volt. Examples of such substituentsinclude, but are not limited to, H, aryl, phenyl, cycloalkyl, alkyl,halogen, alkoxy, alkylthio, perfluoroalkyl, perfluoroaryl, pyridyl,cyano, thiocyanato, nitro, amino, alkylamino, acyl, sulfoxyl, sulfonyl,imido, amido, and carbamoyl. Particular examples of compounds ofFormulas XX and XXI containing annulated arenes are exemplified byFormulas XXII-XXV below.

To link the sandwich coordination compound to a substrate, or to anothercompound such as another sandwich coordination compound in the mannersdescribed above, at least one ligand in the sandwich coordinationcompound will have to contain at least one substituent S¹ through S^(n)or S′ which is a linker, particularly a linker containing a reactivegroup (where multiple linkers are substituted on the ligand, the linkersmay be the same or independently selected). Such linkers are designatedas X-Q- herein, where: Q is a linker, and X is a substrate, a reactivesite or group that can covalently couple to a substrate, or a reactivesite or group that can ionically couple to a substrate.

Q may be a linear linker or an oblique linker, with linear linkerscurrently preferred. Examples of oblique linkers include, but are notlimited to, 4,3′-diphenylethyne, 4,3′-diphenylbutadiyne, 4,3′-biphenyl,1,3-phenylene, 4,3′-stilbene, 4,3′-azobenzene, 4,3′-benzylideneaniline,and 4,3″-terphenyl. Examples of linear linkers include, but are notlimited to, 4,4′-diphenylethyne, 4,4′-diphenylbutadiyne, 4,4′-biphenyl,1,4-phenylene, 4,4′-stilbene, 1,4-bicyclooctane, 4,4′-azobenzene,4,4′-benzylideneaniline, and 4,4″-terphenyl.

X may be a protected or unprotected reactive site or group on the linkersuch as a thio, seleno or telluro group.

Thus, examples of linear linkers for X-Q- are:4-(2-(4-mercaptophenyl)ethynyl)phenyl, 4-mercaptomethylphenyl,4-hydroselenophenyl, 3-(2-4-hydroselenopenyl)ethynyl)phenyl,4-hydrotellurophenyl, and 4-(2-(4-hydrotellurophenyl)ethynyl)phenyl.Examples of oblique linkers for X-Q- are:3-(2-(4-mercaptophenyl)ethynyl)phenyl, 3-mercaptomethylphenyl,3-hydroselenophenyl, 3-(2-(4-hydroselenopenyl)ethynyl)phenyl,3-hydrotellurophenyl, and 3-(2-(4-hydrotellurophenyl)ethynyl)phenyl.

Other suitable linkers include, but are not limited to,2-(4-mercaptophenyl)ethynyl, 2-(4-hydroselenophenyl)ethynyl, and2-(4-hydrotellurophenyl)ethynyl.

Examples of ligands that contain annulated arenes as described aboveinclude,

but are not limited to, ligands of Formula XXII, XXIII, XXIV and XXVbelow:

wherein each substituent S′ is independently selected and preferablyprovides a redox potential of less than about 5, 2 or even 1 volt.Examples of such substituents include, but are not limited to, H, aryl,phenyl, cycloalkyl, alkyl, halogen, alkoxy, alkylthio, perfluoroalkyl,perfluoroaryl, pyridyl, cyano, thiocyanato, nitro, amino, alkylamino,acyl, sulfoxyl, sulfonyl, imido, amido, and carbamoyl. Again, to linkthe sandwich coordination compound to a substrate, or to anothercompound such as another sandwich coordination compound in the mannersdescribed above, at least one ligand in the sandwich coordinationcompound will have to contain at least one substituent S′ which is alinker, particularly a linker containing a reactive group (wheremultiple linkers are substituted on the ligand, the linkers may be thesame or independently selected). Such linkers are as described above.

B. Double-decker and Triple-decker Molecules for Memory Storage.

The double- or triple-decker porphyrinic sandwich molecules can beattached to an electroactive surface in one of several ways. A preferredattachment strategy involves the use of a thiol linker, which can beappended either to the phthalocyanine or porphyrin unit. These examplesare shown in FIG. 7A, which afford a vertical arrangement of themacrocycles with respect to the surface of the electroactive material.Related approaches afford a horizontal orientation as shown in FIG. 7B.Note that the requisite synthetic components, ethynyl porphyrins andethynyl phthalocyanines, are available (R. Wagner et al., J. Am. Chem.Soc. 1996, 118, 11166-11180; M. Ravikanth et al., Tetrahedron 1998, 54,7721-7734; Maya et al., (1999), Chem. Eur. J. 5, 2004-2013)). It haspreviously been demonstrated that thiol-derivatized porphyrins andthiol-derivatized ferrocenes can be attached to electroactive surfaces(Gryko, D. T.; Clausen, P. C.; Lindsey, J. S., J. Org. Chem. 1999, 64,8635-8647; S. Sachs et al., J. Am. Chem. Soc. 1997, 119, 10563-10564; S.Creager et al., J. Am. Chem. Soc. 1999, 121, 1059-1064). Thethiol-derivatized porphyrins were designed for horizontal or verticalorientation with respect to the surface of the electroactive material.

Each of the triple deckers shown in FIG. 7 enables four chargedoxidation states to be accessed. With the neutral state defined as zero,the four charged oxidation states provide a means of counting from 0 to4.

In order to store additional information in a single memory location,two triple deckers can be employed. The oxidation potentials of the twotriple deckers shown in FIG. 8 are given in Table 1. (J. Jiang et al.,Inorg. Chim. Acta 1998, 268, 49-53). In each case four charged oxidationstates are accessible, and the two triple deckers have potentials offsetfrom one another.

TABLE 1 Oxidation potentials of triple deckers. E_(1/2) (V)^(a) Tripledecker I Triple decker II E_(OX)(1) 0.23 0.40 E_(OX)(2) 0.62 0.77E_(OX)(3) 0.95 1.09 E_(OX)(4) 1.23 1.35 ^(a)In Volts vs. Ag/Ag⁺ (valuesfrom the literature are scaled appropriately for this electrode).

These triple deckers can be employed in a mixed assembly, where equalamounts of triple decker I and II are utilized in a given memorylocation. In this manner, eight distinct and different charged oxidationstates can be accessed due to the interleaving of oxidation potentialsof the respective triple-decker molecules. In order to attach thesemolecules to an electroactive surface, a thiol linker is employed asshown in FIG. 9.

A family of such molecules can be created. Tuning of the oxidationpotentials can be achieved by variation in the nature of the porphyrinmeso-substituents, the porphyrin β-substituents, the phthalocyaninesubstituents (R=alkyl, perfluoroalkyl, alkoxy, alkylthio, etc.),replacement of the skeletal atoms of the porphyrin or phthalocyaninemacrocycles, and the nature of the two sandwiched metals (M¹, M²). It isunderstood that such variations in molecular structure (not displayed inthe Figures) can be utilized in order to tune the electrochemicalpotentials as desired.

C. More Elaborate Architectures for Memory Storage.

The same interleaving of oxidation potentials can be achieved with othertriple-decker molecules. In order to access multiple states in amolecular architecture, thereby sidestepping the formation of mixedmonolayers, the triple-decker sandwich molecules can be covalentlylinked, as illustrated in Formula XV and Formula XVI. One example isillustrated in FIG. 10. Here both of the triple deckers are directlyattached to the electroactive surface via the thiol linkers, affording ahorizontal orientation. In FIG. 11, a vertical orientation is achievedwith only one of the two triple deckers directly attached to theelectroactive surface. In each case shown in FIGS. 7 and 8, eightcharged oxidation states can be accessed through interleaving of theoxidation potentials of the two triple-decker molecules. The tuning ofthe potentials is achieved by variation in the nature of thephthalocyanine substituents (R), peripheral groups attached to theporphyrin, skeletal atom replacements in the porphyrin and thephthalocyanine, and in addition different metals as described above canbe employed (Eu is displayed).

Other architectures can be employed where one triple decker issubstituted with redox-active groups such as porphyrins or ferrocenes,as illustrated in Formula XIII and Formula XIV above. Examples aredisplayed in FIGS. 12 and 13. In FIG. 12, one porphyrin bears fourdifferent meso-substituents, of which one includes a protected thiolunit for ultimate attachment to an electroactive surface. The remainingthree meso-substituents are redox-active units, including twosubstituted ferrocene molecules and one porphyrin molecule. Theseredox-active units are chosen so that their oxidation potentials areinterleaved with that of the triple-decker sandwich unit. Variouslinkers can be used to attach the ferrocene units to the porphyrin. Ap-phenylene unit (n=0) and a 4,4′-diphenylethyne unit (n=1) are shown.The selection of the linkers is based on synthetic feasibility and theelectronic communication properties of the linkers. The choice ofp-phenylene or diarylethyne linker is not expected to altersignificantly the intrinsic electrochemical properties of the ferroceneor porphyrin units. The anticipated oxidation states are listed in Table2 (S. Yang et al., J. Porphyrins Phthalocyanines 1999, 3, 117-147).Successive oxidation of the respective units occurs at increasingelectrochemical potential.

TABLE 2 Oxidation potentials of the triple-decker architecture displayedin FIG. 12. E_(1/2) (V)^(a) Redox-active unit −0.05 Pentamethylferrocene(Ar¹) +0.23 Triple decker, first oxidation +0.39 Chloroferrocene (Ar²)+0.62 Triple decker, second oxidation +0.78 Zn-porphyrin, firstoxidation +0.95 Triple decker, third oxidation +1.08 Zn-porphyrin,second oxidation +1.23 Triple decker, fourth oxidation ^(a)In Volts vs.Ag/Ag⁺ (values from the literature are scaled appropriately for thiselectrode).

FIG. 13 displays a related architecture that employs a(Por)Eu(Pc)Eu(Por) triple decker rather than a (Por)Eu(Pc)Eu(Pc)architecture used in FIG. 12. A major distinction is that the(Por)Eu(Pc)Eu(Pc) architecture shifts the first and second oxidationpotential (but not the third or fourth) to lower potential by about100-200 mV. This distinction can be exploited in synthetic design wherethe substituents are selected to have oxidation potentials thatinterleave appropriately with those of the triple-decker unit.

D. Sandwich Compounds as Building Blocks for Constructing FunctionalMaterials: Synthetic Approaches.

Dyads. The synthesis of dyads of triple deckers can proceed via severaldifferent types of reactions. A general issue is that the reaction usedto join the triple deckers into a dyad architecture also generallycreates the linker that provides electronic communication between thetwo triple deckers. Accordingly, a more limited set of reactions isgenerally envisaged than that in the entire corpus of organic chemistry.The reactions of interest include Glaser (or Eglinton) coupling of twoidentical triple deckers (generating a butadiyne linker),Cadiot-Chodkiewicz coupling of two different triple deckers (generatinga butadiyne linker), Sonogashira coupling of two different tripledeckers (generating an ethyne linker), Heck or Wittig reactions of twodifferent triple deckers (generating an alkene linker), Suzuki couplingof two different triple deckers (generating a phenylene or biphenyllinker), etc. We have employed the Glaser coupling and the Sonogashiracoupling with suitably functionalized triple deckers. Other reactionscan also be employed.

Polymers. The synthesis of polymers of triple deckers is of greatinterest, affording materials that have the intrinsic electronicproperties of monomeric triple deckers yet in a molecular frameworkwhere (1) electronic communication among triple deckers (and anelectrode) can be achieved effectively and (2) the polymeric tripledecker materials can be processed using techniques of the polymerindustry.

The methods for synthesis of polymeric arrays of triple deckers includebut are not restricted to use of the following types of reactions:

Glaser (or Eglinton) coupling of a monomeric triple decker (generating abutadiyne linker)

Cadiot-Chodkiewicz coupling of two different triple deckers (generatinga butadiyne linker joining a block copolymer)

Sonogashira coupling of two different triple deckers (generating anethyne linker joining a block copolymer)

Heck or Witting reactions of two different triple deckers (generating analkene linker joining a block copolymer)

Suzuki coupling of two different triple deckers (generating a phenyleneor biphenyl linker joining a block copolymer)

We also can polymerize triple deckers bearing substituents such as twoor more thiophene groups (generating an oligothiophene linker) or two ormore pyrrole groups (generating a polypyrrole linker).

The synthesis of the polymers can be performed using stepwise methods orusing polymerization methods. Both methods generally require tworeactive groups attached to the triple decker in order to prepare apolymer where the triple deckers are integral components of the polymerbackbone. (An alternative design yields pendant polymers where thetriple deckers are attached via one linkage to the polymer backbone.)The stepwise synthetic method generally requires the use of protectinggroups to mask one reactive site, and one cycle of reactions theninvolves coupling followed by deprotection. In the polymerization methodno protecting groups are employed and the polymer is prepared in aone-flask process.

The polymerizations can take place in solution or can be performed withthe polymer growing from a surface. The polymerization can be performedbeginning with a solid support as in solid-phase peptide or DNAsynthesis, then removed, purified, and elaborated further for specificapplications. The polymerization can also be performed with the nascentpolymer attached to an electroactive surface, generating the desiredelectronic material in situ.

Gradient polymers. Polymers can be created that are composed ofidentical units, or dissimilar units as in block copolymers or randomcopolymers. Alternatively, the polymerization can be performed to createa linear array where the composition of different triple deckers isorganized in a gradient. This latter approach affords the possibility ofcreating a molecular capacitor where the potential of stored chargeincreases (or decreases) in a systematic manner along the length of thearray. Such molecular capacitors may find application in the following:

(a) novel information storage materials where the information is storedin the distinct and different oxidation potentials. For example, alinear array can be composed where the lowest potential triple deckersare situated far from the electroactive surface and higher potentialtriple deckers are located close to an electroactive surface. Then ahigh potential oxidation sweep is required to oxidize all the tripledeckers in the array (proximal and distal), but changing to a lowpotential then reduces the proximal triple deckers leaving only thedistal low potential triple deckers in an oxidized state. In so doingthe intervening neutral triple deckers (proximal) constitute a barrierto electron flow, thereby increasing the retention time of stored chargein the oxidized (distal) triple deckers.

(b) electrochromic materials where at fixed potential the color of thearray changes with distance.

(c) molecular batteries. Novel features of the polymeric triple deckersas batteries are as follows: (1) Charge migration occurs along thepolymeric backbone, mediated by the linker joining the triple deckercomponents. Accordingly, diffusive motion of charge carriers is notrequired for charge (hole-hopping, electron transfer) to reach theelectrode. (2) The potential can be tuned by use of substituents,metals, and type of triple decker components in the polymer. (3) Thepolymers discharge in a succession of discrete potentials as defined bythe electrochemical potentials of the individual oxidation states of thetriple decker components. This latter feature accrues from the fact thatthe oxidation potentials of the triple deckers in a polymer areindependent of the oxidation state of neighboring triple deckers. It isunderstood that the fabrication of a battery derived from polymerictriple deckers includes the use of an electrolyte. Such electrolytes caninclude small molecules or polymers.

The gradient polymers are created in the following manner. Apolymerizable unit (triple decker or linker) is attached to a surface(solid resin as for solid-phase syntheses, or an electroactive surface).The first triple decker (TD¹) is added and the coupling reagents areadded in order to perform the polymerization (e.g., a Glaser coupling).Then the solid-phase is washed to remove the coupling reagents (copperreagents in the case of the Glaser coupling) and any unreacted TD¹. Thenthe second triple decker (TD²) is added followed by coupling reagentsand the polymerization is allowed to continue. The same wash procedureis performed again and then the third triple decker (TD³) is addedfollowed by coupling reagents and the polymerization is allowed tocontinue. Repetition of this process enables the systematic constructionof a linear array of triple deckers with graded oxidation potentials.The final polymer is then cleaved from the solid phase (if the resin isemployed for synthesis) or used directly (if the synthesis is performedon an electroactive surface).

The polymerizable groups can be any of the type described above usingthe various name reactions (Glaser, Sonogashira, Cadiot-Chodkiewicz,Heck, Wittig, Suzuki, etc.). The final polymeric product is comprised ofdomains of the various triple deckers [(TD^(i))_(n)] joined via linkersin a linear array.

E. Additional Information on Specific Reaction Types.

Preparation of Symmetrical Butadiyne-linked Triple-deckers.

Glaser Coupling. This coupling reaction, discovered by Glaser over acentury ago (Glaser, C. Ber. 1869, 2, 422), is still very commonly usedto prepare symmetrical butadiynes by the coupling of terminal ethynes. Avariety of conditions can be employed.

(1) Copper reagent. Originally the organic cuprous derivative wasisolated first and then oxidized. Later, it was found that the cuprousderivative can be formed in situ. The portion of cuprous salt whichcould be employed successfully may vary from 0.2 to 600% of thetheoretical amount. Catalytic quantities (0.2%-0.5%) of cuprous saltsare employed mostly with hydrophilic ethynes. Generally, the ratio ofethyne to Cu⁺ should be kept higher than 1. Ammonium or amine compoundsshould also be present (Cameron, M. D.; Bennett, G. E. J. Org. Chem.1957, 22, 557).

(2) Oxidizing agents. Air and oxygen are most frequently employed asoxidizing agents. Other oxidizing agents such as potassium ferricyanide,hydrogen peroxide, and cupric salts have also been employed (Viehe, H.G. Ed: Chemistry of Acetylene, Marcel Dekker, New York, 1969, p. 597).It has been proved, however, in all cases, that the cupric ion is thetrue oxidizing agent (Eglinton, G.; McCrae, W. Adv. Org. Chem. 1963, 4,225).

(3) Time and temperature. In general, room temperature is sufficient andalso convenient. The reaction time varies between minutes and hours.

(4) Solvents. Pyridine is a good solvent for ethynes and their cuprousderivatives. Tertiary amides are also excellent solvents and increasethe coupling speed with a stoichiometric quantity of cuprous salt.However, many kinds of solvents have been successfully employed for theindividual ethynes.

(5) Ethynes. The method is applicable to almost all symmetricalcouplings, no matter what the functional groups are. Yields are good andappear to be limited mostly by the instability of the butadiyne-linkedmaterials formed in the reaction However, this coupling method cannot beapplied to ethynes with strongly complexing functional groups (such asphosphine), or certain metal derivatives, which are unstable under thesereaction conditions (Bohlmann, F. Ber. 1951, 84, 545).

This conventional self-coupling of terminal ethynes has been modified by(1) Pd(0)-CuI catalyzed self-coupling in the presence of chloroacetoneand benzene (Rossi, R.; Carpita, A.; Bigelli, C. Tetrahedron Lett. 1985,523), (2) Pd(II)Cu(I) catalyzed self-coupling in the presence ofstoichiometric iodine (Liu, Q.; Burton, D. J.; Tetrahedron Lett. 1997,38, 4371), (3) Reaction of lithium dialkyl diarylborates with iodine(Pelter, A.; Smith, K.; Tabata, M. J. Chem. Soc. Chem. Commun. 1975,857).

The following diagram shows an example of the Glaser coupling to yield adyad of triple deckers and an example yielding a polymer of tripledeckers. In each case the intervening linker contains a butadiyne unit.

Recently, we have employed the modified Glaser coupling (Pd(II)-Cu(I)catalyzed self-coupling in the presence of stoichiometric iodine) toprepare triple decker dyads with a butadiyne linkage, and the desiredproduct was obtained in good yield (89%) under very mild conditions(room temperature). Under similar conditions, it is expected that thecorresponding functional polymers and/or oligomers with triple deckerunits could also be prepared.

Eglinton Coupling. This method was based on the fact that in Glasercouplings, the true oxidizing agents are cupric salts. In 1956, Eglintonand Galbraith proposed the method which involves a cupric salt oxidationin pyridine (Eglinton, G.; Galbraith, A. R. Chem. Ind. 1956, 737.). Thiscondition was modified by Breslow in the middle 1980s (O'Krongly, D.;Denmeade, S. R.; Chiang, M. Y.; Breslow, R. J. Am. Chem. Soc. 1985, 107,5544), which employed cupric/cuprous couples in oxygen free pyridine.This method is very commonly used today. Pyridine has been mostlyemployed as a good solubilizing and buffering agent. Other amines canalso be employed, such as morpholine and tetramethylethylenediamine. Inaddition, other solvents can also be added. The reaction speed increaseswith the acidity of the acetylenic proton; alkyl ethynes react slowerthan aryl ethynes and butadiynes as in Glaser coupling. The cuprousderivative does not form in significant quantities but appears to be thereaction intermediate.

Straus Coupling. Under conditions of Glaser coupling in acidic media, anenyne can be formed, as first demonstrated by Straus in 1905 (Straus, F.Liebigs Ann. 1905, 342, 190). The original experimental process consistsof refluxing for a few hours, then an acetic acid solution of a drycuprous derivative is added under an inert gas. The only enyne formed ishead-to-tail coupled, whereas the head-to-head coupled enyne could neverbe detected.

Preparation of Unsymmetrical Butadiyne-linked Materials:Cadiot-Chodkiewicz Coupling

For the preparation of unsymmetrical butadiynes, Glaser coupling of twodifferent terminal ethynes inevitably gives a mixture of butadiynes. TheCadiot-Chodkiewicz coupling method, proposed in 1957 (Chodkiewicz, W.Ann. Chim. 1957, 2, 819), provides a directed route to couple twodifferent ethyne units. The Cadiot-Chodkiewicz coupling method consistsof the condensation of ethynes with halogenated ethynes in the presenceof cuprous salt and a suitable amine. It is noteworthy that under thereaction conditions, 1-halogenoethynes can undergo a self-coupling tothe corresponding symmetrical butadiynes (Chodkiewicz, W. Ann. Chim.1957, 2, 819):

(1) Cuprous Salt. The cuprous ethyne derivative is assumed to be thereactive intermediate. The cuprous species is regenerated in thecondensation and can be employed in catalytic amounts (about 1-5%). Thislow concentration of cuprous ion reduces almost entirely theself-coupling of the halogenoethynes.

(2) Basic Agent. This reaction does not occur in acid media. A base isnecessary to neutralize the acid resulting from the condensation. Aminesare good solvents which hinder the self-coupling reaction as well asoxidation of the reaction medium. The efficiency of amines decreases asfollows: primary>secondary>tertiary.

(3) Solvent. Good solubility of the terminal ethyne in the reactionmedium is required. A minimum solubility of the cuprous derivative isalso essential. Alcohols are frequently employed for aryl ethynes.Ethers can be used with scarcely soluble compounds. Tertiary amides arevery good solvents for terminal ethynes and for cuprous derivatives, andare often employed with scarcely soluble compounds.

(4) Nature of the 1-halogenoacetylene. Among chloro-, bromo- andiodo-derivatives the 1-bromoethynes are the most suitable. Generally the1-bromoethynes are sufficiently reactive toward derivatives. At theother extremes, 1-iodoethynes are strongly oxidizing toward the cuprousion and favor the self-coupling reaction, while 1-chloroethynes exhibitlow reactivity.

Suzuki Coupling. Suzuki cross coupling of aryl halides with arylboronicacids has emerged as an extremely powerful tool to form biaryl compounds(For reviews, see: (a) Miyaura, N.; Suzuki, A. Chem. Rev. 1995, 95,2457. (b) Suzuki, A. J. Organomet. Chem. 1999, 576, 147). Thismethodology has been extensively studied with respect to palladiumsources, ligands, additives, solvents etc. (Littke, A. F.; Fu, G. C.Angew. Chem., Int. Ed. 1998, 37, 3387). To date, the compoundscontaining a biaryl linkage could be prepared under very mild conditionsin very good yield with a wide range of substituents under therespective coupling conditions.

Oligomers and/or polymers containing triple decker units with biaryllinkages under Suzuki coupling conditions may be prepared. These kindsof polymers are expected to display interesting optical and/orelectronic properties and thus find applications as functionalmaterials. We have prepared various triple decker building blocksbearing aryl halide groups, while the stable nature of boronic acids(thermally, air and moisture stable) makes it feasible to prepare thecorresponding triple decker building blocks bearing boronic acid groups.The triple decker monomers containing halides and boronic acid groupsare thus treated under Suzuki coupling conditions to afford the desiredmolecular architecture.

D. Sonogashira coupling. The Sonogashira coupling of an ethyne and anaryl halide affords the corresponding ethyne-linked compound. TheSonogashira reaction can be performed using Pd(PPh₃)₂Cl₂ and CuI indilute solution in toluene and triethylamine under mild temperatures(35° C.), or using Pd₂(dba)₃ with tri-o-tolylphosphine in toluene andtriethylamine under mild temperatures (35° C.). Other amine-containingsolvents can be employed as well.

E. Wittig reaction. The Wittig reaction involves the coupling of analkyl halide and an aldehyde or ketone, generating an alkene. This isone of the most powerful methods of carbon-carbon bond formation andinvolves treatment of the alkyl halide with a phosphine (e.g.,triphenylphosphine) followed by treatment with a strong base (e.g.,n-butyl lithium) and reaction with the carbonyl compound.

F. Molecular Architectures for Counting to 8.

One of our objectives is to construct molecular devices capable ofstoring multiple bits of information. Our general approach involvesstoring information in the distinct oxidation states of redox-activemolecules located in a self-assembled monolayer on an electroactivesurface. The ability to store multiple bits requires molecules ormolecular arrays having a large number of accessible oxidation states.Toward that goal, we have investigated a wide variety of redox-activemolecules such as ferrocenes and porphyrins as well as arrays comprisedof multiple redox-active units. Triple-decker phthalocyaninato andporphyrinato sandwich complexes of lanthanides and related metals,comprised of highly delocalised macrocycles held in close proximity, areattractive for molecular-based information storage given their multiple,accessible oxidation states. Such triple-decker complexes generallyexhibit four oxidation potentials in the range 0.1-1.4 V (vs Ag/Ag⁺)corresponding to formation of the monocation, dication, trication andtetracation, as well as a corresponding set of anionic states (J. Jiang,et al., Inorg. Chim. Acta 1998, 268, 49-53). The cationic states aremore attractive than the anionic states given the greater stability ofthe former under real-world conditions.

With a triple decker sandwich complex attached to an electroactivesurface, the ability to access four cationic oxidation states providesfor counting from one to four (where the neutral state is zero). Withtwo triple deckers each having four non-overlapping oxidationpotentials, it becomes possible to count to eight. Such a combination oftriple deckers enables the storage of three bits of information and canbe used as an octal counter. In one design, the two triple deckers arejoined in a covalent architecture bearing one or more linkers such as athiol linker. In another design, the two triple deckers are separatelyfunctionalized with a linker and both derivatized triple deckersco-deposited in a single memory location. The proper functioning of suchan octal counter hinges in large part on the design of the respectivetriple deckers such that the oxidation potentials are different anddistinguishable. The most attractive approach is for the oxidationpotentials of the two triple deckers to be interleaved in a comb-likefashion.

As described in Example 1 herein, we have developed the syntheticmethodology for preparing triple-decker sandwich molecules of generalstructure (Pc)Eu(Pc)Eu(Por) with a thiol-derivatized linker appended tothe porphyrin unit. The thiol-derivatized linker provides a site forattachment of the triple decker to an electroactive surface such asgold. The general synthetic approach is compatible with substituentsattached to the porphyrin and/or phthalocyanine units. While much isknown about the electrochemical properties of metalloporphyrins, theliterature on triple deckers is far less extensive and systematic (D. Ngand J. Jiang, Chem. Soc. Rev. 1997 26, 433-442). In order to understandhow to employ substituents for the control of oxidation potentials inthe triple decker complexes, we elected to prepare a small systematiclibrary of triple deckers of general formula (Pc)Eu(Pc)Eu(Por) and(Por)Eu(Pc)Eu(Por). We felt that the characterization of theelectrochemical properties of this library would facilitate the rationaldesign of an octal counter as well as related molecular devices builtaround triple decker sandwich molecules for multi-bit informationstorage.

In Example 2 we describe results at developing an octal counter. Wefirst describe the synthesis of a library of triple-decker complexeswith electron donating groups attached to the porphyrin and/orphthalocyanine moieties. Next we report the solution electrochemicalstudies of this family of triple-decker complexes. From these resultshas emerged suitable combinations of substituents that provide effectiveinterleaving of oxidation potentials of the triple decker complexes.These insights prompted the synthesis of several thiol-derivatizedtriple deckers that appeared to have suitable electrochemical propertiesfor use in co-deposition experiments leading to multi bit informationstorage. We anticipate that these two triple deckers will enable sevendistinct charged oxidation states to be accessed due to the interleavingof oxidation potentials.

G. Molecular Architectures for Counting to 10.

Yet another architecture for molecular information storage builds on theconcepts of using triple-decker molecules with interleaved oxidationpotentials in conjunction with the use of other redox-active molecules.Such compounds are generally illustrated in Formula XVII and FormulaXVIII above. The example architecture shown in FIG. 14 incorporates twotriple-decker sandwich molecules and two ferrocenes. Altogether thisarchitecture (or other suitable architectures within Formula XVII orFormula XVIII) has available 10 positively charged oxidation states.Note that with the neutral state defined as zero, the charged states ofmonocation to decacation correspond naturally to the numbers from 0 to10. Thus a molecule having this architecture can be used to store anumber from 0 to 10 by setting the electrochemical potential (of themolecules attached to an electroactive surface in a memory location) atthe appropriate potential.

Preferably, the different and distinguishable oxidation states of themolecule, and a storage medium comprising the molecule, can be set by avoltage difference no greater than about 2 volts.

As indicated above, the storage medium is juxtaposed in the proximity ofthe electrode of an apparatus of the invention such that electrons canpass from said storage medium to said electrode. The storage medium maybe juxtaposed to a dielectric material embedded with counterions.Typically, the storage medium and the electrode are fully encapsulatedin an integrated circuit. In one embodiment, the storage medium iselectronically coupled to a second electrode that is a referenceelectrode. The storage medium may be present on a single plane of adevice, and may be present at a multiplicity of storage locations in thedevice. In another embodiment, the storage locations are present onmultiple planes of the apparatus. Each storage location may be addressedby a single electrode, two electrodes, or more. In an assembled devicethe electrodes may be connected to a voltage source such as the outputof an integrated circuit, and/or the electrode may be connected to adevice to read the oxidation state of said storage medium (e.g., avoltammetric device, an amperometric device, a potentiometric device).Such a device may be a sinusoidal voltammeter. The device may provide aFourier transform of the output signal from said electrode. Theapparatus may be assembled or programmed to refresh the oxidation stateof said storage medium after reading said oxidation state.

V. Synthesis and Characterization of Storage Medium Molecule(s)

A. Designing Oxidation States into the Storage Medium Molecule(s).

Control over the hole-storage and hole-hopping properties of theredox-active units of the storage molecules used in the memory devicesof this invention allows fine control over the architecture of thememory device.

Such control is exercised through synthetic design. The hole-storageproperties depend on the oxidation potential of the redox-active unitsor subunits that are themselves or that are used to assemble the storagemedia used in the devices of this invention. The hole-storage propertiesand redox potential can be tuned with precision by choice of basemolecule(s), associated metals and peripheral substituents (Yang et al.(1999) J. Porphyrins Phthalocyanines, 3: 117-147).

For example, in the case of porphyrins, Mg porphyrins are more easilyoxidized than Zn porphyrins, and electron withdrawing or electronreleasing aryl groups can modulate the oxidation properties inpredictable ways.

The electrochemical properties of a library of monomeric Mg or Znporphyrins bearing diverse aryl groups have been characterized (Yang etal. (1999) J. Porphyrins Phthalocyanines, 3: 117-147). The effects ofmetals on metalloporphyrin oxidation potentials are well known (Fuhrhopand Mauzerall (1969) J. Am. Chem. Soc., 91: 4174-4181). Together, theseprovide a strong foundation for designing devices with predictablehole-storage properties.

Ferrocene oxidation potentials can be tuned over a range of nearly 1 Vthrough use of substituents attached to the cyclopentadienyl rings(Encyclopedia of Electrochemistry of the Elements, Bard, A. J., Lund,H., Eds., Marcel Dekker: New York, 1979, Vol. 13, pp 3-27).

The design of compounds with predicted redox potentials is well known tothose of ordinary skill in the art. In general, the oxidation potentialsof redox-active units or subunits are well known to those of skill inthe art and can be looked up (see, e.g., Encyclopedia ofElectrochemistry of the Elements, supra). Moreover, in general, theeffects of various substituents on the redox potentials of a moleculeare generally additive. Thus, a theoretical oxidation potential can bereadily predicted for any potential data storage molecule. The actualoxidation potential, particularly the oxidation potential of theinformation storage molecule(s) or the information storage medium can bemeasured according to standard methods. Typically the oxidationpotential is predicted by comparison of the experimentally determinedoxidation potential of a base molecule and that of a base moleculebearing one substituent in order to determine the shift in potential dueto that particular substituent. The sum of such substituent-dependentpotential shifts for the respective substituents then gives thepredicted oxidation potential.

B. Synthesis of Storage Medium Molecules.

The basic synthetic methodologies used to construct multiporphyrinnanostructures related to this invention are described in Prathapan etal. (1993) J. Am. Chem. Soc., 115: 7519-7520, Wagner et al. (1995) J.Org. Chem., 60: 5266-5273, Nishino et al. (1996) J. Org. Chem., 61:7534-7544, Wagner et al. (1996) J. Am. Chem. Soc., 118: 11166-11180,Strachan et al. (1997) J. Am. Chem. Soc., 119: 11191-11201, and Li etal. (1997) J. Mater. Chem., 7: 1245-1262. These papers describe variousstrategies for the synthesis of a number of multiporphyrin (porphyrinicmacrocycle) compounds. More particularly, these papers which focus onlight capture, energy funneling, and optical gating, have led to thepreparation of nanostructures containing up to 21 covalently linkedporphyrins (Fenyo et al. (1997) J. Porphyrins Phthalocyanines, 1: 93-99,Mongin et al. (1998) J. Org. Chem., 63: 5568-5580, Burrell and Officer(1998) Synlett 1297-1307, Mak et al. (1998) Angew. Chem. Int. Ed. 37:3020-3023, Nakano et al. (1998) Angew. Chem. Int. Ed. 37: 3023-3027, Maket al. (1999) Chem. Commun., 1085-1086). Two-dimensional architectures,such as molecular squares (Wagner et al. (1998) J. Org. Chem., 63:5042-5049), T-shapes (Johnson, T. E. (1995), Ph.D. Thesis, CarnegieMellon University), and starbursts (Li et al. (1997) J. Mater. Chem., 7:1245-1262) all comprised of different covalently linked porphyrinconstituents, have also been prepared.

In addition, the hole storage and dynamic hole mobility characteristicsof the multiporphyrin nanostructures have been investigated in detailduring the course of our other studies of these materials (Seth et al.(1994) J. Am. Chem. Soc., 116: 10578-10592, Seth et al. (1996) J. Am.Chem. Soc., 118: 11194-11207, Strachan et al. (1997) J. Am. Chem. Soc.,119: 11191-11201; Li et al. (1997) J. Mater. Chem., 7: 1245-1262,Strachan et al. (1998) Inorg. Chem., 37: 1191-1201, Yang et al. (1999)J. Am. Chem. Soc., 121: 4008-4018).

A handful of methods are available for forming phthalocyanines((Lindsey, J. S. In The Porphyrin Handbook; Kadish, K. M.; Smith, K.;Guilard, R., Eds.; Academic Press, San Diego, Calif. 1999, Vol. 1, pp45-118)). The lithium pentoxide method (involving the reaction of aphthalonitrile in n-pentanol containing lithium pentoxide) is one of theoldest methods for preparing phthalocyanines (Barrett, P. A.; Frye, D.A.; Linstead, R. P. J. Chem. Soc. 1938, 1157-1163.). This methodsomewhat fell into disuse upon the advent of the Shiraishi method, whichhas been used for the preparation of phthalocyanines bearing largesubstituents (Snow, A. W.; Jarvis, N. L. J. Am. Chem. Soc. 1984, 106,4706-4711; Okur, A. I. et al., Synth. React. Inorg. Met .- Org. Chem.1990, 20, 1399-1412; Rihter, B. D. et al., Photochem. Photobiol. 1992,55, 677-680; Kobayashi, N. et al., Chem. Lett. 1992, 2031-2034; vanNostrum, C. F. et al., Angew. Chem. Int. Ed. Eng. 1994, 33,2173-2175;Linssen, T. G. et al., J. Chem. Soc., Chem. Commun. 1995, 103-104; Duro,J. A. et al., Tetrahedron Lett. 1995, 36, 8079-8082; van Nostrum, C. F.et al., J. Am. Chem. Soc. 1995, 117, 9957-9965; Yilmaz, I.; Bekaroglu,Ö. Chem. Ber. 1996,129, 967-971; Kimura, M. et al., Chem. Commun. 1997,1215-1216; Brewis, M. et al., Chem. Eur. J. 1998, 4, 1633-1640; Kimura,M. et al., Tetrahedron Lett. 1998, 39, 8471-8474; González, A. et al.,Tetrahedron Lett. 1999, 40, 3263-3266). However, phthalonitriles bearingshort alkylethynyl or tetrathiafulvalene-linked substituents wererecently converted to the corresponding phthalocyanines using thelithium pentoxide method (Terekhov, D. S. et al., J. Org. Chem. 1996,61, 3034-3040; Wang, C. et al., J. Chem. Soc., Perkin Trans. 2, 1997,1671-1678). The Shiraishi method and the lithium pentoxide method haveboth been used to prepared (porphyrin)₄phthalocyanine and(porphyrin)₈phthalocyanine star-shaped arrays (Li, J.; et al., J. Org.Chem. 1999, 64, 9090-9100; Li, J. J. Org. Chem. 1999, 64, 9101-9108).For these porphyrin-phthalocyanine arrays, the lithium pentoxide methodgave higher yields than the Shiraishi method. Pd-coupling methods andother coupling methods have been used to prepareporphyrin-phthalocyanine dyads (Yang, S. I. et al., J. Mater. Chem.2000, 10, 283-296; S. Gaspard et al., J. Chem. Soc., Chem. Commun.,1986, 1239; T.-H. Tran-Thi, et al., J. Phys. Chem., 1989, 93, 1226;T.-H. Tran-Thi et al., J. Chim. Phys., 1991, 88, 1151; L. Li, et al., J.Chem. Soc., Chem. Commun., 1991, 619; H. Tian et al., J. Photochem.Photobiol. A: Chem., 1993, 72, 163; K. Dou et al., J. Lumin., 1994, 465;H. Tian et al., Chin. J. Chem., 1996,14, 412; X. Li et al., Chin. J.Chem., 1998, 16, 97; T.-H. Tran-Thi, Coord. Chem. Rev., 1997, 160, 53).

The general synthetic strategy involves the following approaches: (1)synthesis of porphyrin and phthalocyanine monomers; (2) conversion ofthe porphyrin and phthalocyanine monomers with appropriate metals intotriple deckers; (3) attachment of a suitable linker to be used forlinking the triple decker to an electroactive surface; and (4) thedirected self-assembly of the resulting nanostructures on theelectroactive surface (e.g., gold electrode).

The following synthetic methods form the foundation for the synthesis ofporphyrin building block structures:

(1) A room temperature one-flask synthesis of meso-substitutedporphyrins (Lindsey et al. (1987) J. Org. Chem. 52: 827-836, Lindsey etal. (1994) J. Org. Chem. 59: 579-587, Li et al. (1997) Tetrahedron, 53:12339-12360).

(2) Incorporation of bulky groups around the porphyrin to achieveenhanced solubility in organic solvents (Lindsey and Wagner (1989) J.Org. Chem. 54: 828-836).

(3) A one-flask synthesis of dipyrromethanes, key building blocks in thesynthesis of porphyrins bearing 2-4 different meso-substituents (Lee andLindsey (1994) Tetrahedron 50: 11427-11440, Littler et al. (1999) J.Org. Chem. 64: 1391-1396).

(4) A synthesis of trans-substituted porphyrins without acidolyticscrambling (Littler et al. (1999) J. Org. Chem., 64: 2864-2872).

(5) A rational synthesis of porphyrins bearing up to 4 differentmeso-substituents (Lee et al. (1995) Tetrahedron 51: 11645-11672; Cho,W.-S. et al., J. Org. Chem. 1999, 64, 7890-7901).

(6) Efficient Pd-mediated coupling reactions (60-80% yields in 1-2 h at35° C.) for constructing diphenylethyne linkers joining the porphyrins(Wagner et al. (1995) J. Org. Chem., 60: 5266-5273; Wagner et al. (1999)Chem. Mater. 11: 2974-2983).

In one embodiment, porphyrin building blocks are synthesized usingmethods described by Wagner et al. (1996) J. Am. Chem. Soc., 118:11166-11180, Strachan et al. (1997) J. Am. Chem. Soc., 119: 11191-11201,Wagner et al. (1996) J. Am. Chem. Soc., 118: 3996-3997, Li et al. (1997)J. Mater. Chem., 7: 1245-1262; Lindsey et al. (1994) Tetrahedron, 50:8941-8968; Wagner et al. (1994) J. Am. Chem. Soc., 116: 9759-9760;Lindsey and Wagner (1989) J. Org. Chem., 54: 828-836; Lee and Lindsey(1994) Tetrahedron, 50: 11427-11440; Wagner et al., (1995) J. Org.Chem., 60: 5266-5273; Lee et al. (1995) Tetrahedron, 51: 11645-11672;Cho, W.-S. et al., J. Org. Chem. 1999, 64, 7890-7901.

In a preferred embodiment, ethynyl-substituted phthalocyanines areprepared as described in Yang, S. I.; Li, J.; Cho, H. S.; Kim, D.;Bocian, D. F.; Holten, D.; Lindsey, J. S. J. Mater. Chem. (2000) 10,283-296, Maya et al. (1999) Chem. Eur. J. 5: 2004-2013, or Terekhov etal. (1996) J. Org. Chem. 61: 3034-3040.

Methodology for selection and manipulation of thiol linkers has beendescribed in Gryko et al. (1999) J. Org. Chem. 64: 8635-8647.

The synthesis of the molecules that form the basis for the storagemolecules is performed using a modular building block approach. Thisapproach employs a stepwise synthesis (rather than polymerization) andyields highly purified and well-characterized products. One approachutilizes a series of redox-active “building blocks” (e.g., a series ofmonomeric porphyrinic macrocycles or ferrocene constituents) that can belinked to the gold substrate that will serve as one of the electrodes inthe chip. Preferred monomeric redox-active units that are prepared havedifferent oxidation potentials that fall in the range from −0.2 to 1.3volts.

Heteroleptic double deckers comprised of different phthalocyanineligands can be synthesized in several different ways. One methodinvolves the reaction of two different dilithium phthalocyanines(Li₂Pc¹) and (Li₂Pc²) with a metal acetate such as Lu(OAc)₃ at reflux inchloronaphthalene for 1 h, affording a statistical mixture of(Pc¹)Lu(Pc¹), (Pc¹)Lu(Pc²), and (Pc²)Lu(Pc²) which then is separatedchromatographically (Pondaven et al. (991) New J. Chem., 15: 515-516).

A stepwise method toward heteroleptic double deckers comprised ofdifferent phthalocyanine ligands affords greater control over theproduct distribution. In this stepwise method, the reaction of a mixtureof Li₂Pc¹ and M(acac)₃.nH₂O in 1,2,4-trichlorobenzene at reflux forseveral hours affords the half-sandwich complex. The latter is thentreated with a phthalonitrile and 1,8-diazabicyclo[5.4.0]undec-7-ene(DBU) and n-pentyl alcohol under reflux, giving the heteroleptic doubledecker (Pc¹)M(Pc²) quite selectively (Jiang et al. (1998) Inorg. Chim.Acta, 268: 141-144, Jiang et al. (1999) J. Porphyrins Phthalocyanines 3:322-328). The same approach beginning with a porphyrin half-sandwichcomplex affords the heteroleptic (Por)M(Pc) double decker (Jiang et al.(1998) Polyhedron 17: 3903-3908).

A distinct approach toward the synthesis of (Por)M(Pc) double deckersachieves some selectivity by employing reaction of (Pc)M(acac) with aporphyrin when the metal cation is quite large (e.g., La—Gd). On theother hand, the reaction of (Por)M(acac) with a phthalocyanine isemployed when the metal cation is smaller (e.g., Er, Lu, and Y) (Chabachet al. (1995) J. Am. Chem. Soc. 117: 8548-8556).

Heteroleptic triple deckers comprised of porphyrins and phthalocyaninescan be synthesized in the following manner. A mixture of free baseporphyrin is treated with M(acac)₃.nH₂O in 1,2,4-trichlorobenzene atreflux for several hours. Then the dilithium salt of phthalocyanine(Li₂Pc) is added and the mixture is refluxed for an additional period.Subsequent chromatography affords the desired (Por)M(Pc)M(Por) and(Pc)M(Pc)M(Por) triple deckers (Jiang et al. (1998) Inorg. Chim. Acta,268: 49-53). This is a very general method with regards to the nature ofthe metal and the substituents on the phthalocyanine, in spite of thedistribution of products formed, and has been used to prepare a widevariety of such triple deckers.

Triple decker complexes with different metals also can be prepared inthe following manner. Reaction of a (Por)M¹(Pc) with a (Por)M²(acac)complex in 1,2,4-trichlorobenzene at reflux for eight hours resulted inthe (Por)M¹(Pc)M²(por) triple decker, with metal combinations of Ce andGd, Ce and Lu, Ce and Y, and La and Y (Chabach et al. (1996) Angew.Chem. Int. Ed. Engl. 35: 898-899.

A new route to triple decker phthalocyanines involves reaction of ametal or an alloy with a phthalonitrile. A notable example is providedby the reaction of Bi₂Se₃ with phthalonitrile, affording the tripledecker (Pc)Bi(Pc)Bi(Pc) (Janczak et al. (1999) Polyhedron, 18:2775-2780).

In one embodiment, the methods for joining the triple deckers intolarger arrays employ Pd-mediated reactions. One example involves thecoupling of iodo-substituted and ethynyl-substituted porphyriniccompounds (Wagner et al. (1995) J. Org. Chem. 60: 5266-5273, Wagner etal. (1999) Chem. Mater. 11: 2974-2983). Alternatively, theCadiot-Chodkiewicz reaction enables unsymmetrical coupling ofethynyl-substituted compounds, affording the unsymmetrically substitutedbutadiyne product (Eastmond and Walton (1972) Tetrahedron Lett. 28:4591-4599, Elbaum et al. (1994) Tetrahedron 50: 1503-1518, Montierth etal. (1998) Tetrahedron 54: 11741-11748, Godt (1997) J. Org. Chem.62:7471-7474). In yet another example, Suzuki coupling can be employedaffording a phenylene or oligophenylene linker (Hensel and Schluter(1999) Chem. Eur. J. 5: 421-429).

A few double deckers or triple deckers with appended functional groupshave been prepared. The appended groups include the following: quinoneattached to a zirconium bis(porphyrin) (Girolami et al. (1996) Angew.Chem. Int. Ed. Engl. 35: 1223-1225), crown ethers attached to a lutetiumbis(phthalocyanine) (Ishikawa and Kaizu (1998) Chem. Lett. 183-184),porphyrin attached to the porphyrin component of a (Pc)Eu(Por)Eu(Pc)triple decker (Arnold and Jiang (1999) Chem. Lett. 483-484).

Using the synthesis strategies exemplified here and in the examples, oneof ordinary skill in the art can routinely produce relatively complexdata storage molecules for use in the devices of this invention.

C. Characterization of the Storage Media.

The storage media molecule(s), once prepared, can be characterizedaccording to standard methods well known to those of skill in the art.The characterization of multiporphyrin nanostructures has been described(see, e.g., Strachan et al. (1997) J. Am. Chem. Soc., 119: 11191-11201;Wagner et al. (1996) J. Am. Chem. Soc., 118: 3996-3997; Li et al. (1997)J. Mater. Chem., 7: 1245-1262; Seth et al. (1996) J. Am. Chem. Soc.,118:11194-11207; Seth et al. (1994) J. Am. Chem. Soc., 116:10578-10592). In a preferred embodiment, the electrochemical studiesinclude cyclic and square-wave voltammetry to establish the redoxpotentials of the monomeric and multi-unit constituents of the storagemedia. Bulk electrochemical oxidations are performed on each of thestorage materials to assess the hole-storage capabilities and thestability. Absorption and vibrational spectroscopic methods are used toassess the structural and electronic properties of both the neutral andoxidized materials. Electron paramagnetic resonance techniques are usedto probe the hole-storage and hole-mobility characteristics of theoxidized storage molecules. Using the above-identified techniques,benchmarks for the expected performance characteristics of a storagemolecule (e.g., oxidation potentials, redox reversibility, dynamichole-mobility characteristics, etc.) can be ascertained.

D. Self-assembly of the Storage Medium Molecules on Target Substrates.

In preferred embodiments, the storage molecules comprising the storagemedium are designed to self-assemble on a substrate (e.g. a metal suchas gold). The disklike structure of the porphyrin macrocycles engendersself-assembly. Self-assembled monolayers of porphyrins on solidsubstrates are well known and have been extensively studied (see, e.g.,Schick et al. (1989) J. Am. Chem. Soc., 111: 1344-1350, Mohwald et al.(1986) Thin Solid Films, 141: 261-275).

To exert control over the pattern of self-assembly, reactive sites (e.g.thiols) or linkers bearing active sites are incorporated into thestorage molecules (nanostructures). The reactive sites bind to thetarget (e.g. gold electrode) surface giving an organized self-assembledstructure. In the case of porphyrins with thiol-derivatized linkersattached to the meso positions, the porphyrins arrange in horizontalorientations. Non-covalent interactions between storage molecules aretypically weak, particularly when bulky aryl groups are attached to eachof the porphyrins.

VI. Writing to the Storage Device

In preferred embodiments of the data storage devices of this invention,information is written to a particular memory location via applicationof a potential of the requisite value and temporal duration at theappropriate working and reference electrode(s) to achieve the desireddigital value. The information can be erased via application of apotential of the opposite sign.

There is a great advantage to the small size of each memory element,which is essentially a modified electrode surface. When each memoryelement is reduced to sub-micron dimensions, the area of the surfaceallows the presence of only a few hundred data storage (e.g., porphyrin)molecules. Using Faraday's law, Q=nFN (where Q equals the total charge,n equals the number of electrons per molecule, F is 96,485 Coulombs/moleand N is the number of moles of electroactive species present), it canbe determined that only a small charge (1.6×10⁻¹⁶ C; if passed in 1 μs,would result in a current of roughly 160 pA) must pass in order tochange the electrochemical charge corresponding to each bit.

Additionally, the intrinsic limitation to the speed of mostelectrochemical experiments lies in the time required to charge theelectrode to the appropriate potential (the charging current, which hasa time dependence of exp(−t/RC)). Since the capacitance of the electrodeis directly proportional to its area, miniaturization of each element ofthe system to submicron dimensions will greatly increase its speed. Forexample, a square gold electrode with 0.1 μm dimensions would have acapacitance of approximately 2×10⁻¹⁹ F, leading to an RC time constantof only 2 picoseconds. For this reason, electrode charging currentsshould be insignificant in determining the ultimate performance of thesedevices.

The voltage used to write the data can be derived from any of a widevariety of sources. In a simple embodiment, the voltage can simply bethe output from a power supply. However, in preferred embodiments, thevoltage will be the output from some element of an electronic circuit.The voltage can be a signal, the representation of a logic state, theoutput from a gate, from an optical transducer, from a centralprocessing unit, and the like. In short, virtually any voltage sourcethat can be electrically coupled to the devices of this invention can beused to write data to the storage media therein.

VII. Reading from the Storage Device

The storage device(s) of this invention can be read according to any ofa wide variety of methods well known to those of ordinary skill in theart. Essentially any method of detecting the oxidation state of acompound can be utilized in the methods of this invention. However,where the readout is destructive of the state of the memory cell(s)(e.g. in certain memories), the read will preferably be followed by arefresh to reset the oxidation state of the storage cell.

In particularly preferred embodiments as shown in FIG. 1 and FIG. 2, thestorage medium 102 of a storage cell 100 is set to neutral (e.g., 0potential for the system, but which might not be at true zero voltagewith respect to ground) using the working electrode. The oxidation stateof the memory cell is then set by changing the potential at thereference electrode 103 (e.g. by setting the reference electrodenegative to the desired voltage). The oxidation state of the storagecell is then measured (e.g. using sinusoidal voltammetry) via theworking electrode 101. In this preferred format, the oxidation state isassayed by measuring current. By measuring current at the workingelectrode 101 and setting the state with the reference electrode 103,the measurement is not made at the place the potential is applied. Thismakes it far simpler to discriminate the oxidation state. If thepotential were applied to the electrode through which the current wasmeasured unnecessary noise would be introduced into the system.

A. Reading from the Storage Media.

In the case of the storage media as described herein, the reading ofinformation from a particular memory location is achieved extremelyrapidly by sweeping a potential over the full range used to establishthe dynamic range of the storage element. The fidelity of themeasurement is dependent on how well the oxidation state of theindividual storage element can be determined. Traditionally,electrochemical methods could only improve the signal to noise ratio bydiscriminating the faradaic signal from the background components in thetime domain through application of pulse waveforms (i.e., differentialpulse polarography, square wave voltammetry). These methods discriminatethe faradaic current from the charging current in the time domain, sincecharging currents decay much more rapidly than the faradaic current(exp(−t/RC) vs t^(−1/2), respectively). However, the analytical faradaiccurrent is not totally discriminated from the charging current, and mostof the signal is discarded because sampling is done late in the pulsecycle.

More recently, sinusoidal voltammetry (SV) has been shown to havesignificant advantages over traditional waveforms in an electrochemicalexperiment (Singhal and Kuhr (1997) Anal. Chem., 69: 1662-1668. Forexample, the background current resulting from cyclic voltammetry(consisting primarily of charging current) resembles a square wave,which contains significant intensity at both fundamental and oddharmonic frequencies. In contrast, the charging current resulting fromsine wave excitation has only one frequency component centered at thefundamental, while the faradaic current is distributed over manyfrequencies. This characteristic of sine wave excitation simplifies theelectroanalytical measurement, since the signal from each oxidationstate can be fine-tuned by “locking-in” on one of the higher frequencyharmonics. Ultimately, the speed at which this can be performed is onlylimited by the kinetics of the redox reaction, which may ultimately leadto megahertz frequency operation.

Since most electrochemical methods rely on differences between theE_(1/2)'s (E_(1/2) is the potential at which half of the subjectmolecules are oxidized or reduced to a particular oxidation state) todifferentiate compounds present in a sample and thereby to generate theselectivity for the measurement, this has severely limited the utilityof electrochemical methods for the analysis of many complex matrices. Incontrast, sinusoidal voltammetry can exploit the vast diversity inelectron transfer rates observable at solid electrodes (k⁰, the rate ofelectron transfer) can vary over ten orders of magnitude at the sameelectrode surface) to obtain additional selectivity in theelectrochemical measurement.

The composition of the frequency spectrum is extremely dependent on therate of electron transfer. By adjusting the frequency of the sinusoidal(or other time-varying) excitation waveform, it becomes possible to usethis kinetic information as well as the phase information todiscriminate between two molecules which have very similarelectrochemical properties. For example, this technique has been usedfor the detection of the direct oxidation of double-stranded DNA atcopper electrodes (Singhal and Kuhr (1997) Anal. Chem., 69: 1662-1668).Where this is usually undetectable at conventional electrodes withstandard voltammetric techniques, the use of sinusoidal voltammetryallowed the measurement of 1.0 nM double-stranded DNA. The concentrationdetection limit (S/N=3) for this size of dsDNA at the 6th harmonic is3.2 pM. When coupled with a low-volume system, such as a monolayer ofthe adsorbed material, this allows detection of sub-zeptomole (10⁻²¹mole) quantities of the storage medium molecule(s) on the surface.

This procedure may ultimately degrade the memory in the absence of arefresh mechanism. The level of degradation will depend on the totalnumber of molecules ultimately used to ensure acceptable faulttolerance. To avoid degradation problems, however, a refresh cycle (awrite cycle resetting the memory to the read value) can be insertedimmediately after each read cycle is complete.

B. Instrumentation for Reading/writing Molecular Memories.

As indicated above, the molecular memory devices can be read by any of awide variety of electrochemical technologies including amperometricmethods (e.g. chronoamperometry), coulometric methods (e.g.chronocoulometry), voltammetric methods (e.g., linear sweep voltammetry,cyclic voltammetry, pulse voltammetries, sinusoidal voltammetry, etc.),any of a variety of capacitance measurements, and the like. Suchreadouts can be performed in the time and/or frequency domain.

In one preferred embodiment, readout is accomplished using a fastpotentiostat/voltammetry system. Such a system is capable of reading andwriting the memory elements on a microsecond time scale. Such a systemcan be modified from a prototypical system described in U.S. Pat. No.5,650,061.

As illustrated in FIG. 16, a potentiostat with an RC time constant lessthan one microsecond is provided by using a fast voltage driver (e.g.,video buffer amplifier). A preferred video buffer amplifier retains ausable bandwidth beyond 20 MHz and is used to rephase the voltage andcurrent in the excitation signal to zero phase shift between voltage andcurrent. This rephasing of the excitation signal immediately before theworking electrode cancels out any phase shift which might be introducedby capacitance in the cable leading from the Arbitrary WaveformSynthesizer (AWS) function generator. An important part of the currentmonitor is a wide band op-amp. By using an op-amp with a very widegain-bandwidth product, the amplifier gain can be set to 10,000 andstill retain a bandwidth usable from DC to above 1 MHz. This allows thecollection of impedance data from electrodes as small as a 1 μm diskover a frequency range from 15 kHz to 5 MHz.

VIII. Use of the Storage Device in Computer Systems

The use of the storage devices of this invention in computer systems iscontemplated. One such computer system is illustrated in FIG. 17. Thecomputer comprises a signal source (e.g. 110 device or CPU), a storagedevice of this invention, and appropriate circuitry (e.g. voltammetrycircuitry) to read the state(s) of the storage device. In operation,voltages representing the bits to be stored are applied to the workingelectrodes of the storage device thereby setting the memory. Whenretrieval is necessary (e.g. for output, or further processing) thestate(s) of the storage device is read by the 110 circuitry and theinformation is passed off to other elements (e.g. CPU) in the computer.

FIG. 17 and FIG. 18 illustrate the memory devices of this inventionintegrated into a standard computer architecture or computer system 200.The hardware of system 200 includes a processor (CPU) 205, a memory 206(which can comprise molecular memory devices), a persistent storage 208which does comprise molecular memory devices of this invention, andhardware for a graphical user interface (GUI) 220, coupled by a localbus or interface 210. The persistent memory 208 can include themolecules shown in FIG. 6. System 200 can further include additionalhardware components (not shown).

System 200 can be, for example, a personal computer or workstation.Processor 205 can be, for example, a microprocessor, such as the 80386,80486 or Pentium™ microprocessor, made by Intel Corp. (Santa Clara,Calif.). Memory 206 can include, for example, random-access memory(RAM), read-only memory (ROM), virtual memory, molecular memory or anyother working storage medium or media accessible by processor 205.Persistent storage 208 can include a hard disk, a floppy disk, anoptical or magneto-optical disk, a molecular memory or any otherpersistent storage medium. GUI 220 facilitates communications between auser and system 200. Its hardware includes a visual display 221 and aselector device (mouse, keyboard, etc.) 222. Through visual display 221,system 200 can deliver graphical and textual output to the user. Fromselector device 222, system 200 can receive inputs indicating theuser'selection of particular windows, menus, and menu items. Visualdisplay 221 can include, for example, a cathode-ray tube (CRT) orflat-panel display screen, or a head-mounted display such as a virtualreality display. Selector device 222 can be, for example, atwo-dimensional pointing device such as a mouse, a trackball, a trackpad, a stylus, a joystick, or the like. Alternatively or additionally,selector device 222 can include a keyboard, such as an alphanumerickeyboard with function and cursor-control keys.

The software of system 200 includes an operating system 250 and anapplication program 260. The software of system 200 can further includeadditional application programs (not shown). Operating system 250 canbe, for example, the Microsoft® Windows™ 95 operating system for IBM PCand compatible computers having or emulating Intel 80386, 80486, orPentium™ processors. Alternatively, the operating system can bespecialized for operation utilizing molecular memory elements.Application program 260 is any application compatible with the operatingsystem and system 200 architecture. Persons of skill in the art willappreciate that a wide range of hardware and software configurations cansupport the system and method of the present invention in variousspecific embodiments.

The present invention is explained in greater detail in the followingnon-limiting examples.

EXAMPLE 1 Synthesis of Thiol-Derivatized Europium PorphyrinicTriple-Decker Sandwich Complexes for Multi-Bit Molecular InformationStorage

In these examples, the synthesis of S-acetylthio derivatizedporphyrin-phthalocyanine triple-decker molecules is described. A set oftriple-decker building blocks bearing trimethylsilyl and/or iodo groupswas also prepared. Two of the triple-decker building blocks were joinedto afford an S-acetylthio derivatized dyad of triple-deckers. All of thesandwich complexes prepared employ europium as the coordination metals.

Results and Discussion

Porphyrin-phthalocyanine triple-decker building blocks. In order toprepare triple-decker complexes for attachment to an electroactivesurface, provisions must be made for incorporation of athiol-derivatized linker. In order to prepare molecular architectureswherein multiple triple deckers are joined together in a controlledmanner, provisions must be made for incorporating synthetic handles onthe triple deckers. In principle the thiol linker and the synthetichandles could be fastened to the porphyrin or the phthalocyanine unit inthe triple deckers. Because the synthetic chemistry of porphyrins ismuch better developed than that of phthalocyanines, triple deckerbuilding blocks that are constructed around suitably functionalizedporphyrins have been developed. To avoid any rotational isomers thatmight accrue from two functionalized porphyrins in one triple decker,molecules comprised of one porphyrin and two phthalocyanines have beenprepared. Two isomers of such a triple decker are possible dependingwhether the porphyrin is located in the middle or at the end of thesandwich. Given the greater yield of the triple decker with theporphyrin on the end of the sandwich (i.e., (Pc)M(Pc)M(Por)), thesynthesis of triple decker building blocks of this general type has beenpursued.

The harsh nature of the reaction conditions for forming triple deckersprecludes incorporation of a protected thiol unit or other sensitivegroups in the porphyrin monomer prior to forming the triple decker.Thus, the preparation of triple deckers bearing an iodo group or anethynyl group, or both an iodo and an ethynyl group, has been a focus.These synthetic handles provide the opportunity for elaboration of thetriple-decker complexes into large molecular arrays or for attachment ofthiol linkers. The porphyrin building blocks to be used in preparing thecorresponding triple-decker building blocks are shown in FIG. 19.

The general procedure for preparing mixed porphyrin-phthalocyaninesandwich complexes involves refluxing the porphyrin with excessM(acac)₃.nH₂O in 1,2,4-trichlorobenzene, affording the(porphyrin)M(acac) complex, followed by the addition of dilithiumphthalocyanine (Li₂Pc) with continued reflux. However, quite differentproduct distributions have been obtained upon reaction under rathersimilar conditions. These include (Por)M(Pc) as the sole product(Chabach, D. et al., J. Am. Chem. Soc. 1995, 117, 8548-8556),(Por)M(Pc)M(Pc) as the sole product (Moussavi, M. et al., Inorg. Chem.1986, 25, 2107-2108), Li[(Pc)M(Por)] as the main product (Jiang, J. etal., Chem. Ber. 1996, 129, 933-936), products including (Por)M(Pc)M(Por)and (Pc)M(Por)M(Pc) (Chabach, D. et al., New J. Chem. 1992, 16,431-433), and products including (Por)M(Pc), (Por)M(Pc)M(Por) and(Por)M(Pc)M(Pc) with the latter two kinds of compounds as the mainproducts (Jiang, J. et al., Inorg. Chim. Acta 1997, 255, 59-64; Jiang,J. et al., Inorg. Chim. Acta 1998, 268, 49-53). The distribution of theproducts appears to depend rather strongly on the nature of the metal aswell as the substituents on the macrocycles.

Treatment of 5-(4-iodophenyl)-15-phenyl-10,20-di(p-tolyl)porphyrin(IPT-Por) with excess Eu(acac)₃.nH₂O in 1,2,4-trichlorobenzene affordedthe corresponding (Por)Eu(acac). Treatment of the latter with Li₂Pc gavea mixture containing (IPT-Por)Eu(Pc)Eu(IPT-Por), (Pc)Eu(IPT-Por)Eu(Pc),(Pc)Eu(Pc)Eu(IPT-Por) as well as traces of (Pc)Eu(IPT-Por) and(Pc)Eu(Pc) (FIG. 20). The mixture could be partially separated by onesilica gel column, affording bands comprised predominantly of(IPT-Por)Eu(Pc)Eu(IPT-Por) contaminated with (Pc)Eu(IPT-Por) andstarting porphyrin (IPT-Por) [band 1], (Pc)Eu(IPT-Por) and startingporphyrin (IPT-Por) [band 2], (Pc)Eu(IPT-Por)Eu(Pc) [band 3],(Pc)Eu(Pc)Eu(IPT-Por) [band 4], and (Pc)Eu(Pc) [top of column]. Furtherpurification of band 1 by passage over one SEC column afforded pure(IPT-Por)Eu(Pc)Eu(IPT-Por). A second silica column of band 4 affordedpure (Pc)Eu(Pc)Eu(IPT-Por). The isolated yields were as follows:(IPT-Por)Eu(Pc)Eu(IPT-Por) (17%), (Pc)Eu(IPT-Por)Eu(Pc) (1%), and(Pc)Eu(Pc)Eu(IPT-Por) (14%). These results are somewhat similar to thoseof Jiang et al., supra though the isolated yield of(IPT-Por)Eu(Pc)Eu(IPT-Por) was substantially lower than the 60% reportedby Jiang et al. for the same kind of triple-decker complex. Furthermore,in addition to triple-decker complex (Pc)Eu(Pc)Eu(IPT-Por), we alsoisolated the isomeric triple-decker complex (Pc)Eu(IPT-Por)Eu(Pc),though in relatively low yield.

The same reaction conditions were employed with three other porphyrinsand analogous product distributions were obtained. The resultsconcerning the isolated yields of triple deckers from each reaction aresummarized in Table 3. In each case no decomposition of the synthetichandles (iodo, TMS-ethyne) was noticed. The stability of thetrimethylsilylethynyl group to these reaction conditions was surprising,given the lability of the TMS group toward base even under very mildconditions (Wagner, R. W. et al., J. Am. Chem. Soc. 1996, 118,11166-11180). This approach afforded a number of building blocktriple-decker complexes of general structure (Pc)Eu(Pc)Eu(Por) as shownin FIG. 21. Deprotection of the TMS-ethynyl group of the triple deckers(Pc)Eu(Pc)Eu(ET-Por) and (Pc)Eu(Pc)Eu(EB-Por) afforded the correspondingethynyl triple deckers (Pc)Eu(Pc)Eu(E′T-Por) and (Pc)Eu(Pc)Eu(E′B-Por),respectively.

TABLE 3 Yields of triple-decker building blocks with variousporphyrins.¹ Isolated Yields (%) (Por)Eu(Pc)Eu- (Pc)Eu(Por)Eu-(Pc)Eu(Pc)Eu- Porphyrin (Por) (Pc) (Por) IPT-Por 17%   1%  14% ET-Por9.5%  0.5% 9.1% EB-Por 26% 1.6% 9.1% IET-Por 19% 1.5% 9.9% ¹Reactionswere performed using a ratio of 1.5 moles of Pc component per 1 mol ofporphyrin. Yields were calculated based on the amount of porphyrin.

Synthesis of thiol-derivatized porphyrin-phthalocyanine triple-deckercomplexes. For applications in molecular information storage devices,the triple-decker complexes must be attached to an electroactivematerial such as a gold surface. Among various thiol protecting groupsthat are cleaved in situ on gold, the S-acetyl group was found to beideal, especially for attachment of porphyrinic compounds (Gryko, D. T.et al., J. Org. Chem. 1999, 64, 8635-8647). Two different approaches forintroducing the S-acetylthio group into the triple-decker nucleus havebeen explored.

In one case, the iodo-substituted triple decker (Pc)Eu(Pc)Eu(IPT-Por)and 4-ethynyl-1-(S-acetylthio)benzene were coupled under Pd-mediatedcoupling conditions (Pd(PPh₃)₂Cl₂, CuI) in the presence of the baseN,N-diisopropylethylamine (FIG. 22). Because the S-acetylthio groupundergoes cleavage in the presence of some of the bases (diethylamine,triethylamine) commonly used in Pd-coupling reactions,N,N-diisopropylethylamine was used (Pearson, D. L.; Tour, J. M. J. Org.Chem. 1997, 62, 103076-1387), and no cleavage product was found in thereaction mixture. Purification via two silica columns gave the desiredS-(acetylthio)-derivatized triple-decker 1 in 50% yield.

Previously, mild conditions for joining iodo and ethynyl-substitutedporphyrin building blocks under Pd-coupling reactions (Pd₂(dba)₃, AsPh₃or tri-o-tolylphosphine) have been developed that avoid use of copperco-catalysts. Copper accelerates Pd-mediated coupling reactions but mustbe omitted in the synthesis of multiporphyrin arrays comprised of freebase porphyrins in order to avoid adventitious metalation (Wagner, R. W.et al., J. Org. Chem. 1995, 60, 5266-5273; Wagner, R. W. et al. Chem.Mater. 1999, 10, 2974-2983). Due to the strong coordination of thelanthanide triple-decker complexes, the usual side-products resultingfrom copper metalation or transmetalation are not expected. Indeed,clean copper-free products were obtained in the presence of copper saltsduring the Pd-coupling reaction.

In a second case, the ethynyl-substituted triple decker(Pc)Eu(Pc)Eu(EB-Por) and 4-iodo-1-(S-acetylthio)benzene were coupledunder the Pd-coupling conditions (Pd₂(dba)₃, tri-o-tolylphosphine) usedfor joining porphyrin building blocks (FIG. 23). It is known that coppercan facilitate homo-coupling leading to the butadiyne-linked product,and such products are minimized under these conditions. Examination ofthe laser desorption mass spectrum of the crude reaction mixturerevealed two dominant peaks (m/z 2179, 2287) corresponding to an unknownspecies and the desired product, respectively. Column chromatographyafforded the two separate species. ¹H NMR analysis of the former speciesrevealed a sharp singlet (2.86 ppm, 3H) consistent with an acetylmoiety. This species was assigned to an acetylated derivative of theethynyl-substituted triple decker starting material. This side reactionis ascribed to the acetylation by 4-iodo-1-(S-acetylthio)benzene (orproduct derived therefrom) of the ethynyl group attached to thetriple-decker complex. The desired S-acetylthio derivatizedtriple-decker 2 was obtained in 19% yield, which is quite low comparedwith the typical yield (50˜60%) in the reaction between two porphyrinmonomers under the same conditions. The simplest way to avoid formingthe acetylated triple decker by-product is to employ an iodo- ratherthan ethynyl-substituted triple-decker complex.

Sonogashira coupling to yield a thiol-derivatized dyad oftriple-deckers. The use of thiol-derivatized triple deckers forinformation storage provides the opportunity to access four cationicstates, thereby storing two bits of information. In order to storeadditional information in one memory storage location, two differenttriple deckers can be employed where the four oxidation potentials ofeach are interleaved in a comb-like manner, accessing eight cationicstates and thereby storing three bits of information. Alternatively, twotriple deckers can be incorporated in one molecular architecture. Thereare at least two advantages of incorporating multiple redox-activegroups in a molecular architecture. (1) The deposition of a homogeneouspopulation of information storage molecules in a memory storage cell isnot subject to fractionation effects as might occur with co-depositionof a mixture of molecules of different types. (2) The positioning ofredox-active units in a vertical stack enables a higher concentration ofredox-active molecules of a given type than would be possible uponco-deposition of a mixture of thiol-derivatized molecules each bearingone redox-active unit in a monolayer. To explore these advantages thesynthesis of a dyad of triple deckers has been pursued.

Two routes to the desired dyad are readily envisaged. In one route, anS-(acetylthio)-substituted ethynyl benzene is coupled with aniodo/TMS-ethynyl triple decker, then after TMS cleavage theS-(acetylthio)-derivatized ethynyl triple decker is reacted with an iodotriple decker. This route introduces the protected thio moiety at theearliest stage of the synthetic plan. A complementary route begins withcoupling of an ethynyl triple decker and iodo/TMS-ethynyl triple deckerto make a dyad followed by TMS cleavage and reaction with anS-(acetylthio)-substituted iodo benzene. The latter route introduces thethiol linker in the last step of the synthetic plan, and is attractivein minimizing handling of the S-(acetyl)-protected thiophenol moiety.This latter route was used in the following synthesis.

Treatment of triple-decker (Pc)Eu(Pc)Eu(IET-Por) with(Pc)Eu(Pc)Eu(E′T-Por) under Pd-mediated coupling conditions(Pd(PPh₃)₂Cl₂, CuI) afforded the desired ethyne-linked dyad along with abutadiyne-linked dyad (FIG. 24A). The two dyads were easily separatedfrom the other components of the reaction mixture by SEC, however, allattempts to separate the ethyne-linked dyad from the butadiyne-linkeddyad were unsuccessful. The mixture of dyads was then treated with K₂CO₃to cleave the trimethylsilyl group. The subsequent coupling with4-iodo-1-(S-acetylthio)benzene afforded the corresponding mixture of theS-acetylthio derivatized dyads. At this stage, the butadiyne-linked dyadresulting from the first coupling reaction was successfully removed. Theethyne-linked dyad was obtained in 3.8% yield. It is interesting that nohomo-coupled dyad was obtained in the reaction with4-iodo-1-(S-acetylthio)benzene; this may be due to the faster reactionof the ethynyl dyad with 4-iodo-1-(S-acetylthio)benzene compared withthe dimerization of ethynyl dyads.

However, in order to avoid the self-coupling of (Pc)Eu(Pc)Eu(E′T-Por),the alternative copper-free coupling conditions (Pd₂(dba)₃, P(o-tol)₃,no copper) were employed to prepare the ethyne-linked dyad (E-dyad-1)(FIG. 24B). We previously prepared a series of multiporphyrin arraysunder these copper-free Pd-mediated coupling conditions and noself-coupling products were observed (R. Wagner et al., Chem. Mater.1999, 10, 2974-2983; R. Wagner et al., J. Am. Chem. Soc. 1996, 118,11166-11180). Thus, treatment of (Pc)Eu(Pc)Eu(IET-Por) with(Pc)Eu(Pc)Eu(E′T-Por) under the copper-free Pd-mediated conditionsafforded the desired ethyne-linked dyad (E-dyad-1) in 44% yield, and nobutadiyne-linked dyad was detected. Treatment of E-dyad-1 with K₂CO₃afforded E′-dyad-1 in 83% yield. The subsequent coupling (Pd(PPh₃)₂Cl₂,CuI) with 1-(S-acetylthio)-4-iodobenzene afforded a mixture containingthe S-acetylthio-derivatized dyad (Dyad-1), the acetylation product ofE′-dyad-1 as well as a trace of self-coupling products derived fromE′-dyad-1. One adsorption column (removal of the acetylation product)followed by one SEC column (removal of the butadiyne-linkedself-coupling byproduct) afforded pure Dyad-1 in 22% yield.

Glaser coupling to yield a butadiyne-linked dyad. We sought to prepare abutadiyne-linked dimer (Dyad-2) in order to (1) investigate thefeasibility of performing a Glaser coupling using ethynyl tripledeckers, and (2) investigate the solution electrochemistry of a dimer oftriple deckers. For the preparation of symmetrical diynes, a modifiedEglinton-Glaser coupling (in the presence of CuCl/CuCl₂) has foundincreasing application (D. O'Krongly et al., J. Am. Chem. Soc. 1985,107, 5544-5545). However, treatment of E′-dyad-1 with CuCl/CuCl₂ in DMFin the absence or presence of an amine at room temperature only gave atrace of the product even after 24 h. The Pd(II)-Cu(I) catalyzedself-coupling of terminal alkynes in the presence of iodine wasintroduced which gives good to excellent yields with a broad range ofterminal alkynes (Q. Liu and D. Burton, Tetrahedron Lett. 1997, 38,4371-4374). Thus, treatment of E′-dyad-1 with Pd(PPh₃)₂Cl₂ and CuI inthe presence of 0.5 mole equiv (per mol of E′-dyad-1) of iodine intoluene/N,N-diisopropylamine (5:1) gave the desired Dyad-2 in 89% yield(FIG. 25). The reaction was clean and the product was easily separatedby a single adsorption column followed by one SEC column.

Characterization of porphyrin-phthalocyanine mixed triple-deckercomplexes. Each triple-decker complex was characterized by LD-MS, UV-Visand ¹H NMR spectroscopy. The UV-Vis spectra of the triple-deckercomplexes of general structure (Pc)Eu(Por)Eu(Por) resemble those ofanalogous triple-deckers (Jiang, J. et al., Inorg. Chim. Acta 1997, 255,59-64; Jiang, J. et al., Inorg. Chim. Acta 1998, 268, 49-53). Theabsorption at 341-354 nm and 415-420 nm can be attributed to thephthalocyanine and porphyrin Soret bands, respectively. The remainingabsorption bands in the visible region were mainly attributed to the Qbands of the phthalocyanines. In moving from (Por)Eu(Pc)Eu(Por) to(Pc)Eu(Pc)Eu(Por), the ratio of Por to Pc decreases from 2 to ½, and theabsorption intensity contributed by the porphyrins also decreasedcorrespondingly. However, the spectra of the complexes are not simplythe sum of the resulting components. For example, in each of the twokinds of above complexes, the absorption at 341-354 nm remains thestrongest owing to the interactions between the macrocycles. On theother hand, the triple-deckers (Pc)Eu(Por)Eu(Pc) have the samecomposition as (Pc)Eu(Pc)Eu(Por) but display different absorptionspectra, indicating different interaction between the macrocycles withrespect to the different structure. The absorption spectra of(Pc)Eu(Por)Eu(Pc) are in agreement with those reported for the same kindof cerium(III) triple-decker complexes (Chabach, D. et al., New J. Chem.1992, 16, 431-433).

LD-MS has been found to be very effective for identifying thecomposition of mixed porpyrin-phthalocyanine sandwich complexes. Spectrawere collected without the traditional aid of matrices. In most cases,the triple-deckers (Por)Eu(Pc)Eu(Por) and (Pc)Eu(Por)Eu(Pc) display onlythe molecular ion peak. In contrast, the triple-decker complexes such as(Pc)Eu(Pc)Eu(Por) exhibit a parent molecular ion peak and two additionalfragment peaks corresponding to [(Pc)Eu(Pc)]⁺ and [Eu(Por)]⁺.

The ¹H NMR spectra of all the triple-decker complexes recorded in CDCl₃gave moderately resolved spectra leading to valuable structuralinformation. The resonance patterns of the triple-deckers(Por)Eu(Pc)Eu(Por) are in accord with those of the same type ofcompounds reported by Jiang et al., supra. The α and β protons of thephthalocyanine sandwiched between the two porphyrins showed highlydeshielded broad signals in the regions δ 12.73-12.75 and 10.65-10.67ppm. The number of signals stemming from the phenyl groups of theporphyrins indicates that there is restricted rotation about theC(meso)-C(phenyl) bond. These results along with the integration areconsistent with the triple-decker structure (Por)Eu(Pc)Eu(Por) in whichtwo paramagnetic metal centers are sandwiched between two outerporphyrin and one inner phthalocyanine macrocycles.

The ¹H NMR data of (Pc)Eu(Pc)Eu(Por) are consistent with theunsymmetrical layered structure of this kind of triple-decker complex.Four broad resonances at δ 12.95-12.98, 11.06-11.11, 10.10-10.13 and8.72-8.75 ppm of comparable intensity result from the α and β protons ofthe two unequivalent phthalocyanines (one inner, one outer). Theunsymmetrical structure was further supported by the LD-MS spectra, inwhich two strong peaks assigned to [(Pc)Eu(Pc)]⁺ and [Eu(Por)]⁺ werealso observed in addition to the molecular ion peaks. This arrangementof macrocycles is in accord with the structure reported for most of theporphyrin-phthalocyanine triple-deckers containing two phthalocyaninesand one porphyrin (Moussavi, M. et al., Inorg. Chem. 1986, 25,2107-2108; Jiang et al., supra).

In contrast, the ¹H NMR spectra of triple-deckers of general structure(Pc)Eu(Por)Eu(Pc) revealed only two peaks at 9.59-9.71 and 8.05-8.22 ppmwith the same intensity assigned to the α and β protons of thephthalocyanines, suggesting the symmetrical structure of the complexes.

All the porphyrin-phthalocyanine sandwich compounds prepared are stableunder the conditions described for synthesis and routine handling.Furthermore, in contrast to the poor solubility of phthalocyanines, theporphyrin-phthalocyanine sandwich complexes display satisfactorysolubility in common organic solvents such as toluene, chloroform andTHF. The improved solubility is ascribed to the layered structure andnon-planar geometry of the end ligands in the triple deckers, whichsuppresses aggregation.

Experimental Section

General. ¹H NMR spectra (300 MHz) and absorption spectra (HP 8451A, Cary3) were collected routinely. Porphyrin-phthalocyanine sandwich complexeswere analyzed by laser desorption (LD-MS) mass spectrometry (BrukerProflex II) and high resolution fast atom bombardment (FAB) on a JEOL(Tokyo, Japan) HX 110HF mass spectrometer. Commercial sources provideddilithium phthalocyanine (Aldrich), Eu(acac)₃.nH₂O (Alfa Aesar) andPd(PPh₃)₂Cl₂ (Aldrich). Unless otherwise indicated, all other reagentswere obtained from Aldrich Chemical Company, and all solvents wereobtained from Fisher Scientific.5-(4-iodophenyl)-15-phenyl-10,20-di(p-tolyl)porphyrin (IPT-Por),5,10,15-tris[(4-tert-butyl)phenyl]-20-[4-(2-(trimethylsilyl)ethynyl)phenyl]porphyrin(EB-Por),5-(4-iodophenyl)-15-[4-(2-(trimethylsilyl)ethynyl)phenyl]-10,20-di(p-tolyl)porphyrin(IET-Por), and5,10,15-tri(p-tolyl)-20-[4-(2-(trimethylsilyl)ethynyl)phenyl]porphyrin(ET-Por) were prepared by a rational synthetic method (Cho et al., 1999,J. Org. Chem. 64, 7890-7901).

Chromatography. Adsorption column chromatography was performed usingflash silica gel (Baker, 60-200 mesh). Preparative-scale size exclusionchromatography (SEC) was performed using BioRad Bio-beads SX-1. Apreparative-scale glass column (4.8×60 cm) was packed using Bio-beadsSX-1 in THF and eluted with gravity flow. Following purification, theSEC column was washed with two volume equivalents of THF.

Solvents. All solvents were dried by standard methods prior to use.CH₂Cl₂ (Fisher, reagent grade) and CHCl₃ (Fisher, certified ACS grade,stabilized with 0.75% ethanol) were distilled from K₂CO₃. THF (Fisher,certified ACS) was distilled from sodium, and triethylamine (Fluka,puriss) was distilled from CaH₂. Pyrrole (Acros) was distilled atatmospheric pressure from CaH₂. All other solvents were used asreceived.

Preparation of triple deckers upon reaction of IPT-Por. A mixture of5-(4-iodophenyl)-15-phenyl-10,20-di(p-tolyl)porphyrin (154 mg, 0.2 mmol)and Eu(acac)₃.nH2O (301 mg, 0.6 mmol) in 1,2,4-trichlorobenzene (40 mL)was heated to reflux and stirred under argon for 4 h. The resultingcherry-red solution was cooled to rt, then Li₂Pc (160 mg, 0.3 mmol) wasadded. The mixture was refluxed for an additional 5 h, then the volatilecomponents were removed under vacuum. The residue was dissolved in CHCl₃and loaded onto a silica gel column packed with the same solvent.Elution with CHCl₃ afforded four bands. The first band (olive-brown)contained mainly the triple-decker complex (IPT-Por)Eu(Pc)Eu(IPT-Por)and unreacted porphyrin starting material. The second band (red)contained mainly porphyrin starting material and traces of thedouble-decker complex (Pc)Eu(IPT-Por). The third band (black) containedthe triple-decker complex (Pc)Eu(IPT-Por)Eu(Pc). The last band (green)contained the triple-decker complex (Pc)Eu(Pc)Eu(IPT-Por) anddouble-decker complex (Pc)Eu(Pc).

The first band collected was redissolved in THF and loaded onto a SECcolumn. Elution with the same solvent afforded(IPT-Por)Eu(Pc)Eu(IPT-Por) as the first band (greenish-brown), whichafter removal of the solvent and washing with CH₃OH afforded agreenish-black solid (40 mg, 17%). ¹H NMR (CDCl₃) δ 2.96 (s, 12H),3.91-3.95 (m, 16H), 4.63-4.86 (m, 8H), 6.56 (m, 4H), 6.76 (m, 2H), 7.09,7.11 (m, 2H), 8.10 (m, 2H), 8.88 (m, 4H), 9.13 (m, 2H), 9.49 (m, 2H),10.65 (bs, 8H), 11.67 (bs, 4H), 11.91 (bs, 2H), 12.73 (bs, 8H); LD-MScalcd av mass for C₁₂₄H₇₈I₂N₁₆Eu₂ 2349.8, obsd 2355.1; λ_(abs) 355, 420,491, 606, 657 nm.

The third band collected was also redissolved in THF and loaded onto aSEC column. Elution with THF afforded (Pc)Eu(IPT-Por)Eu(Pc) as thesecond band (black), which after removal of the solvent and washing withCH₃OH afforded a black solid (4 mg, 1%). ¹H NMR (CDCl₃) δ 4.13 (s, 6H),8.08 (bs, 16H), 8.35 (s, 1H), 9.58 (bs, 16H), 9.91 (bs, 5H), 10.11 (m,2H), 10.47 (m, 2H), 11.96 (bs, 8H), 13.90-14.09 (m, 7H); LD-MS calcd avmass for C₁₁₀H₆₃IN₂₀Eu₂ 2095.7, obsd 2098.1; λ_(abs) 343, 444, 517, 626,652 nm.

The last band (green) collected was redissolved in toluene and loadedonto a short silica gel column packed with the same solvent. Elutionwith toluene afforded the first band (greenish-blue) containing(Pe)Eu(Pc)Eu(IPT-Por), which after removal of the solvent and washingwith CH₃OH afforded a green solid (59 mg, 14%). ¹H NMR (CDCl₃) δ 2.98(s, 6H), 3.18, 3.22 (m, 8H), 4.72-4.92 (m, 4H), 6.55 (d, J=7.2 Hz, 2H),6.75 (t, J=7.2 Hz, 1H), 7.12 (d, J=7.5 Hz, 1H), 8.14 (m, 1H), 8.73 (bs,8H), 9.08 (m, 2H), 9.29 (m, 1H), 9.68 (m, 1H), 10.11 (bs, 8H), 11.08(bs, 8H), 12.19 (bs, 3H), 12.40 (m, 1H), 12.96 (bs, 8H); LD-MS calcd avmass for C₁₁₀H₆₃IN₂₀Eu₂ 2095.7, obsd 2098.8 (M⁺), 1177.8[M⁺-(IPT-Por)Eu], 919.3 (M⁺-(Pc)Eu(Pc)); λ_(abs) 342, 414, 522, 617, 721nm.

Preparation of triple deckers upon reaction of EB-Por. A mixture of5,10,15-tris[4-(tert-butyl)phenyl]-20-[4-(2-(trimethylsilyl)ethynyl)phenyl]porphyrin(88 mg, 0.10 mmol) and Eu(acac)₃.nH₂O (150 mg, 0.3 mmol) in1,2,4-trichlorobenzene (20 mL) was heated to reflux and stirred underargon for 4 h. The resulting cherry-red solution was cooled to rt, thenLi₂Pc (80 mg, 0.15 mmol) was added. The mixture was refluxed for anadditional 5 h, then the solvents were removed under vacuum. The residuewas dissolved in CHCl₃, and loaded onto a silica gel column packed withthe same solvent. Elution with CHCl₃ afforded four bands. The first band(olive-brown) contained mainly the triple-decker complex(EB-Por)Eu(Pc)Eu(EB-Por) and unreacted porphyrin starting material. Thesecond band (red) contained mainly porphyrin starting material and atrace of double-decker complex (Pc)Eu(EB-Por). The third band (black)contained triple-decker complex (Pc)Eu(EB-Por)Eu(Pc). The last band(green) contained triple-decker complex (Pc)Eu(Pc)Eu(EB-Por) anddouble-decker complex (Pc)Eu(Pc).

The first band collected was redissolved in THF and loaded onto a SECcolumn. Elution with the same solvent afforded (EB-Por)Eu(Pc)Eu(EB-Por)as the first band (greenish-brown), which after removal of the solventand washing with CH₃OH afforded a greenish-black solid (34 mg, 26%). ¹HNMR (CDCl₃) δ 0.62 (s, 18H), 1.89 (s, 54H), 3.83-4.03 (m, 16H), 4.76 (m,9H), 6.71 (m, 6H), 6.84 (m, 2H), 9.00 (bs, 6H), 9.19 (m, 2H), 10.65 (bs,8H), 11.46-11.60 (m, 8H), 12.73 (bs, 8H); LD-MS calcd av mass forC₁₅₄H₁₃₆N₁₆Si₂Eu₂ 2571.0, obsd 2574.1; λ_(abs) 355, 421, 493, 559, 606nm.

The third band collected was also redissolved in THF and loaded onto aSEC column. Elution with THF afforded (Pc)Eu(EB-Por)Eu(Pc) as the secondband (black), which after removal of the solvent and washing with CH₃OHafforded a black solid (3.5 mg, 1.6%). ¹H NMR (CDCl₃) δ 0.85 (s, 18H),2.89, 2.94 (m, 26H), 8.05 (bs, 16H), 9.59 (bs, 16H), 9.99 (m, 2H), 10.10(m, 4H), 11.98-12.20 (m, 4H), 13.52 (m, 2H), 13.68 (m, 4H); LD-MS calcdav mass for C₁₂₅H₉₄N₂₀SiEu₂ 2206.2, obsd 2209.1; λ_(abs) 343, 416, 519,625, 653 nm.

The last band (green) collected was redissolved in toluene and loadedonto a short silica gel column packed with the same solvent. Elutionwith toluene afforded the first band (greenish-blue)(Pc)Eu(Pc)Eu(EB-Por), which after removal of the solvent and washingwith CH₃OH afforded a green solid (20 mg, 9.1%). ¹H NMR (CDCl₃) δ 0.68(s, 9H), 1.86 (m, 27H), 3.20-3.29 (m, 8H), 4.71-4.91 (m, 4H), 6.67 (m,3H), 6.91 (m, 1H), 8.72 (bs, 8H), 9.08-9.16 (m, 3H), 9.41 (m, 1H), 10.10(bs, 8H), 11.10 (bs, 8H), 11.69 (m, 2H), 11.88 (m, 1H), 12.16 (m, 1H),12.97 (bs, 8H); LD-MS calcd av mass for C₁₂₅H₉₂N₂₀SiEu₂ 2206.2, obsd2117.1 (M⁺), 1181.4 [M⁺-(EB-Por)Eu], 919.3 (M⁺-(Pc)Eu(Pc)); λ_(abs) 342,417, 522, 552, 618, 721 nm.

Preparation of triple deckers upon reaction of IET-Por. A mixture of5-(4-iodophenyl)-15-[4-(2-(trimethylsilyl)ethynyl)phenyl]-10,20-di(p-tolyl)porphyrin(261 mg, 0.30 mmol) and Eu(acac)₃nH₂O (450 mg, 0.9 mmol) in1,2,4-trichlorobenzene (60 mL) was heated to reflux and stirred underargon for 4 h. The resulting cherry-red solution was cooled to rt, thenLi₂Pc (240 mg, 0.45 mmol) was added. The mixture was refluxed for anadditional 5 h, then the solvents were removed under vacuum. The residuewas dissolved in CHCl₃ and loaded onto a silica gel column packed withthe same solvent. Elution with CHCl₃ afforded four bands. The first band(olive-brown) contained mainly the triple-decker complex(IET-Por)Eu(Pc)Eu(IET-Por) and unreacted porphyrin starting material.The second band (red) contained mainly porphyrin starting material andtrace amount of double-decker complex (Pc)Eu(IET-Por). The third band(black) contained triple-decker complex (Pc)Eu(IET-Por)Eu(Pc). The lastband (green) contained triple-decker complex (Pc)Eu(Pc)Eu(IET-Por) anddouble-decker complex (Pc)Eu(Pc).

The first band collected was redissolved in THF and loaded onto a SECcolumn. Elution with the same solvent afforded(IET-Por)Eu(Pc)Eu(IET-Por) as the first band (greenish-brown), whichafter removal of the solvent and washing with CH₃OH afforded agreenish-black solid (72 mg, 19%). ¹H NMR (CDCl₃) δ 0.64 (s, 18H), 2.98(s, 12H), 3.91 (m, 16H), 4.66-4.74 (m, 6H), 4.84, 4.86 (m, 2H), 6.58 (d,J=5.7 Hz, 4H), 6.92 (d, J=5.7 Hz, 2H), 7.15 (m, 2H), 8.97 (d, J=5.7 Hz,4H), 9.36 (d, J=5.1 Hz, 2H), 9.58 (d, J=5.1 Hz, 2H), 10.67 (bs, 8H),11.85 (m, 6H), 12.08 (m, 2H), 12.76 (bs, 8H); LD-MS calcd av mass forC₁₃₄H₉₄N₁₆I₂Si₂Eu₂ 2542.2, obsd 2547.5; λ_(abs) 356, 421, 493, 606 nm.

The third band collected was also redissolved in THF and loaded onto aSEC column. Elution with THF afforded (Pc)Eu(IET-Por)Eu(Pc) as thesecond band (black), which after removal of the solvent and washing withCH₃OH afforded a black solid (10 mg, 1.5%). ¹H NMR (CDCl₃) δ 1.16 (s,9H), 4.15 (s, 6H), 7.21 (s, 4H), 8.22 (bs, 16H), 9.71 (bs, 16H), 9.94(bs, 4H), 10.26 (m, 2H), 10.46 (m, 2H), 11.97 (m, 6H), 13.94-14.14 (m,6H); LD-MS calcd av mass for C₁₁₅H₇₁N₂₀ISiEu₂ 2191.8, obsd 2192.5;λ_(abs) 341, 444, 517, 628, 656, 796 nm.

The last band (green) collected was redissolved in toluene and loadedonto a short silica gel column packed with the same solvent. Elutionwith toluene afforded the first band (greenish-blue) containing(Pc)Eu(Pc)Eu(IET-Por), which after removal of the solvent and washingwith CH₃OH afforded a green solid (65 mg, 9.9%). ¹H NMR (CDCl₃) δ 0.69(s, 9H), 1.60 (s, 6H), 3.01-3.20 (m, 8H), 4.78 (m, 4H), 5.01 (m, 1H),6.56 (m, 2H), 6.95 (m, 2H), 8.75 (bs, 8H), 9.12 (m, 2H), 9.57 (m, 1H),9.76 (m, 1H), 10.12 (bs, 8H), 11.11 (bs, 8H), 12.29-12.42 (m, 2H), 12.66(m, 1H), 12.98 (bs, 8H); LD-MS calcd av mass for C₁₁₅H₇₁N₂₀ISiEu₂2191.8, obsd 2195.1 (M⁺), 1181.4 [M⁺-(IET-Por)Eu], 919.3(M⁺-(Pc)Eu(Pc)); λ_(abs) 342, 417, 522, 552, 618, 721 nm.

Preparation of triple deckers upon reaction of ET-Por. A mixture of5,10,15-tri(p-tolyl)-20-[4-(2-(trimethylsilyl)ethynyl)phenyl]porphyrin(140 mg, 0.19 mmol) and Eu(acac)₃nH₂O (280 mg, 0.57 mmol) in1,2,4-trichlorobenzene (35 mL) was heated to reflux and stirred underargon for 4 h. The resulting cherry-red solution was cooled to rt, thenLi₂Pc (220 mg, 0.29 mmol) was added. The mixture was refluxed for anadditional 5 h, then the solvents were removed under vacuum. The residuewas dissolved in CHCl₃ and loaded onto a silica gel column packed withthe same solvent. Elution with CHCl₃ afforded four bands. The first band(olive-brown) contained mainly (ET-Por)Eu(Pc)Eu(ET-Por) and unreactedporphyrin starting material. The second band (red) contained mainlyporphyrin starting material and traces of double-decker complex(Pc)Eu(ET-Por). The third band (black) contained triple-decker complex(Pc)Eu(ET-Por)Eu(Pc). The last band (green) contained triple-deckercomplex (Pc)Eu(Pc)Eu(ET-Por) and double-decker complex (Pc)Eu(Pc).

The first band collected was redissolved in THF and loaded onto a SECcolumn. Elution with THF afforded (ET-Por)Eu(Pc)Eu(ET-Por) as the firstband (greenish-brown), which after removal of the solvent and washingwith CH₃OH afforded a greenish-black solid (21 mg, 9.5%). ¹H NMR (CDCl₃)δ 0.64 (s, 18H), 2.99 (s, 18H), 3.86-3.96 (m, 16H), 4.77-4.89 (m, 8H),6.58 (bs, 6H), 6.92 (m, 2H), 8.97 (bs, 6H), 9.35 (bs, 2H), 10.65 (bs,8H), 11.90-12.08 (m, 8H), 12.75 (bs, 8H); LD-MS calcd av mass forC₁₃₆H₁₀₀N₁₆Si₂Eu₂ 2318.5, obsd 2321.9; λ_(abs) 355, 420, 491, 606, 657nm.

The third band collected was also redissolved in THF and loaded onto aSEC column. Elution with THF afforded (Pc)Eu(ET-Por)Eu(Pc) as the secondband (black), which after removal of the solvent and washing with CH₃OHafforded a black solid (2 mg, 0.5%). ¹H NMR (CDCl₃) δ 1.10 (s, 9H), 4.17(s, 9H), 8.11 (bs, 16H), 9.62 (bs, 16H), 9.92 (m, 7H), 10.26 (m, 2H),11.92-11.99 (m, 8H), 13.95-14.50 (m, 7H); LD-MS calcd av mass forC₁₁₆H₇₄N₂₀SiEu₂ 2080.0, obsd 2083.7; λ_(abs) 341, 444, 517, 628, 656,796 nm.

The last band (green) collected was redissolved in toluene and loadedonto a short silica gel column packed with the same solvent. Elutionwith toluene afforded the first band (greenish-blue) containing(Pc)Eu(Pc)Eu(ET-Por), which after removal of the solvent and washingwith CH₃OH afforded a green solid (36 mg, 9.1%). ¹H NMR (CDCl₃) δ 0.69(s, 9H), 3.00 (m, 9H), 3.15 (m, 8H), 4.83 (d, J=7.2 Hz, 2H), 4.89 (d,J=7.2 Hz, 1H), 5.03 (d, J=7.2 Hz, 1H), 6.56 (t, J=7.2 Hz, 3H), 6.96 (d,J=7.2 Hz, 1H), 8.74 (bs, 8H), 9.11 (m, 3H), 9.53, 9.55 (m, 1H), 10.13(bs, 8H), 11.06 (bs, 8H), 12.30-12.42 (m, 3H), 12.62 (m, 1H), 12.95 (bs,8H); LD-MS calcd av mass for C₁₁₆H₇₄N₂₀SiEu₂ 2080.0, obsd 2083.2 (M⁺),1178.3 [M⁺-(ET-Por)Eu], 903.1 (M⁺-(Pc)Eu(Pc)); λ_(abs) 342, 417, 522,552, 618, 721 nm.

Formation of (Pc)Eu(Pc)Eu(E′T-Por). A sample of (Pc)Eu(Pc)Eu(ET-Por) (33mg, 0.016 mmol) was dissolved in CHCl₃/CH₃OH (6 mL, 3:1). K₂CO₃ (20 mg,0.14 mmol) was added, and the reaction mixture was stirred at rt underargon with occasional monitoring by ¹H NMR spectroscopy. Uponcompletion, CHCl₃ (30 mL) was added to the reaction mixture, and theresulting mixture was washed with NaHCO₃ (10%, 2×30 mL), H₂O (30 mL),dried (Na₂SO₄), filtered, and rotary evaporated to dryness. Columnchromatography (silica, CHCl₃) afforded a black solid (31 mg, 97%). ¹HNMR (CDCl₃) δ 3.03 (m, 9H), 3.17, 3.24 (m, 8H), 3.72 (s, 1H), 4.83 (m,3H), 5.00 (d, J=8.1 Hz, 1H), 6.56 (m, 3H), 6.96 (d, J=7.2 Hz, 1H), 8.77(bs, 8H), 9.13 (m, 3H), 9.53, 9.55 (m, 1H), 10.18 (bs, 8H), 11.14 (bs,8H), 12.22-12.32 (m, 3H), 12.50 (m, 1H), 13.03 (bs, 8H); LD-MS calcd avmass for C₁₁₃H₆₆N₂₀Eu₂ 2007.8, obsd 2008.6 (M⁺), 1177.4[M⁺-(E′T-Por)Eu], 831.0 (M⁺-(Pc)Eu(Pc)); λ_(abs) 342, 416, 521, 618, 721nm.

Formation of (Pc)Eu(Pc)Eu(E′B-Por). A sample of (Pc)Eu(Pc)Eu(EB-Por) (20mg, 0.0091 mmol) was treated with K₂CO₃ and worked-up following the sameprocedure as for (Pc)Eu(Pc)Eu(E′T-Por). Column chromatography (silica,CHCl₃) afforded a black solid (18 mg, 94%). ¹H NMR (CDCl₃) δ 1.95, 1.97(m, 27H), 3.30-3.38 (m, 8H), 3.71 (s, 1H), 4.77 (d, J=7.2 Hz, 3H), 5.00(d, J=6.6, 1H), 6.70 (m, 3H), 6.95 (d, J=7.2 Hz, 1H), 8.76 (bs, 8H),9.09-9.16 (m, 3H), 9.39, 9.41 (m, 1H), 10.16 (bs, 8H), 11.17 (bs, 8H),11.56 (m, 2H), 11.73 (m, 1H), 12.00 (m, 1H), 13.04 (bs, 8H); LD-MS calcdav mass for C₁₂₂H₈₄N₂₀Eu₂ 2134.1, obsd 2136.5 (M⁺); λ_(abs) 343, 415,522, 552, 618, 722 nm.

S-acetylthio-derivatized triple decker (1). Samples of(Pc)Eu(Pc)Eu(IPT-Por) (30 mg, 14 μmol),4-ethynyl-1-(S-acetylthio)benzene (20 mg, 0.11 mmol), Pd(PPh₃)₂Cl₂ (1.5mg, 2.1 μmol) and CuI (0.19 mg, 1.0 μmol) were added to a 25 mL Schlenkflask. The flask was evacuated and purged with argon three times. Thendeaerated THF (5 mL) and deaerated N,N-diisopropylethylamine (1 mL) wereadded by syringe. The flask was immersed in an oil bath at 30° C. andstirred under argon. The reaction was monitored by TLC (silica, toluene)and LD-MS. After 20 h, the solvent was removed under vacuum, the residuedissolved in toluene/CHCl₃ (1:1), and loaded onto a silica gel columnpacked with the same solvent. Elution with toluene/CHCl₃ (1:1) affordedunreacted starting material and a deep green second band, whichcontained the desired product and also a minor amount of the startingmaterial. The product thus obtained was further purified by a secondcolumn chromatography procedure (silica gel, toluene), affording a blacksolid (15 mg, 50%) after removal of the solvent and washing with CH₃OH.¹H NMR (CDCl₃) δ 2.62 (s, 3H), 2.99 (s, 6H), 3.20 (bs, 8H), 4.82 (d,J=7.5 Hz, 2H), 4.96 (d, J=6.6 Hz, 1H), 5.05 (d, J=6.0 Hz, 1H), 6.56 (d,J=7.5 Hz, 2H), 6.77 (m, 1H), 6.99 (m, 1H), 7.74 (d, J=7.8 Hz, 2H), 8.05(d, J=8.1 Hz, 2H), 8.16 (t, J=8.0 Hz, 1H), 8.73 (bs, 8H), 9.07 (m, 2H),9.31 (m, 1H), 9.56 (m, 1H), 10.10 (bs, 8H), 11.08 (bs, 8H), 12.21 (m,2H), 12.42 (m, 1H), 12.51 (m, 1H), 12.96 (bs, 8H); LD-MS calcd av massfor C₁₂₀H₇₀OSN₂₀Eu₂ 2144.0, obsd 2146.2 (M⁺), 2104.2 (M⁺-CH₃CO), 1178.4(M⁺-(IPT-Por)Eu), 968.2 (M⁺-(Pc)Eu(Pc)), 925.4 (M⁺-(Pc)Eu(Pc)-CH₃CO);λ_(abs) 342, 416, 521, 618, 720 nm.

S-acetylthio-derivatized triple decker (2). Samples of(Pc)Eu(Pc)Eu(E′B-Por) (15 mg, 7.0 mol), 4-iodo-1-(S-acetylthio)benzene(2.0 mg, 7.0 μmol), Pd₂(dba)₃ (1.0 mg, 1.1 μmol) and P(o-tolyl)₃ (2.5mg, 8.3 μmol) were added to a Schlenk flask. The flask was evacuated andpurged with argon three times. Then deaerated toluene (3 mL) anddeaerated N,N-diisopropylethylamine (0.6 mL) were added by syringe. Theflask was immersed in an oil bath at 35° C. and stirred under argon. Thereaction was monitored by TLC (silica, toluene) and LD-MS. After 24 h,the solvent was removed under vacuum, the residue dissolved intoluene/ether (60:1), and loaded onto a silica gel column packed withthe same solvent. Elution with toluene/ether (60:1) afforded the desiredproduct together with trace of unreacted starting material as the firstband. The product thus obtained was further purified by a second columnchromatography procedure (silica gel, toluene), affording a black solid(3.1 mg, 19%) after removal of the solvent and washing with CH₃OH. ¹HNMR (CDCl₃) δ 1.90, 1.92 (m, 27H), 2.62 (s, 3H), 3.28 (m, 8H), 4.70-4.80(m, 3H), 4.98 (d, J=6.6 Hz, 1H), 6.68 (m, 4H), 6.94 (d, J=6.6 Hz, 1H),7.54 (m, 1H), 7.71 (m, 1H), 8.03 (m, 1H), 8.71 (bs, 8H), 9.05-9.12 (m,3H), 9.42 (m, 1H), 10.10 (bs, 8H), 11.11 (bs, 8H), 11.56 (m, 2H), 11.72(m, 1H), 12.02 (m, 1H), 12.98 (bs, 8H); LD-MS calcd av mass forC₁₃₀H₉₀OSN₂₀Eu₂ 2284.3, obsd 2191.4 (M⁺), 2250.2 (M⁺-CH₃CO), 1181.0(M⁺-(Por)Eu), 1111.6 (M⁺-(Pc)Eu(Pc)), 1067.8 (M⁺-(Pc)Eu(Pc)-CH₃CO);λ_(abs) 341, 419, 523, 618, 721 nm.

E-dyad-1. Samples of (Pc)Eu(Pc)Eu(IET-Por) (35 mg, 16 μmol),(Pc)Eu(Pc)Eu(E′T-Por) (32 mg, 16 μmol), Pd₂(dba)₃ (2.3 mg, 2.5 μmol) andP(o-tol)₃ (5.8 mg, 19 μmol) were reacted in the presence of toluene (5mL) and triethylamine (1 mL) at 35° C. using a Schlenk line. Thereaction was monitored by analytical SEC and LD-MS. After 15 h, thesolvent was removed and the residue was dissolved in CHCl₃ and loadedonto a silica gel column packed in CHCl₃. Elution with CHCl₃ afforded amain green band, which was concentrated to dryness, redissolved intoluene, and loaded onto a preparative SEC column packed with the samesolvent. Elution with toluene afforded two well separated green bands,of which the second band was collected. Removal of the solvent andwashing with CH₃OH afforded a black solid (28.5 mg, 44%). ¹H NMR δ 0.79(s, 9H), 3.11, 3.16 (m, 15H), 3.36-3.61 (m, 16H), 5.00, 5.02 (m, 5H),5.20 (m, 1H), 5.48 (m, 2H), 6.71, 6.74 (d, J=7.5 Hz, 5H), 7.10 (m, 1H),7.57 (m, 2H), 8.91 (brs, 16H), 9.25 (m, 6H), 9.68 (m, 1H), 10.09, 10.14(m, 2H), 10.29 (brs, 16H), 11.30 (brs, 16H), 12.31-12.42 (m, 4H), 12.75,12.85 (m, 2H), 13.04 (brs, 1H), 13.18 (brs, 16H); LD-MS obsd 4074.2(M⁺); FAB-MS obsd 4072.72, calcd exact mass 4072.85 (C₂₂₈H₁₃₆SiN₄₀Eu₄);λ_(abs) 343, 425, 521, 617, 666, 720 nm.

E′-dyad-1. A sample of E-dyad-1 (22 mg, 5.4 μmol) in CHCl₃/THF/CH₃OH (8mL, 1:5:2) was treated with K₂CO₃ (20 mg, 0.14 mmol). The reactionmixture was stirred at rt under argon with occasional monitoring by ¹HNMR spectroscopy and LD-MS. Upon completion, CHCl₃ (30 mL) was added andthe resulting mixture was washed with 10% aq NaHCO₃, H₂O, dried(Na₂SO₄), filtered, and concentrated. Column chromatography (silica,CHCl₃) afforded a black solid (18 mg, 83%). ¹H NMR δ 3.08-3.10 (m, 15H),3.29-3.59 (m, 16H), 3.74 (s, 1H), 4.97 (m, 5H), 5.13 (m, 1H), 5.44 (m,2H), 6.69 (d, J=7.2 Hz, 5H), 7.21 (m, 1H), 7.54 (m, 2H), 8.86 (brs,16H), 9.19 (brs, 6H), 9.58 (m, 1H), 10.18 (m, 2H), 10.25 (brs, 16H),11.25 (brs, 16H), 12.23-12.36 (m, 4H), 12.52 (m, 1H), 12.82 (m, 2H),13.14 (brs, 16H); LD-MS obsd 4008.3 (M⁺); FAB-MS obsd 4001.09, calcdexact mass 4000.81 (C₂₂₅H₁₂₈N₄₀Eu₄); λ_(abs) 343, 421, 523, 618, 667,721 nm.

Dyad-1. Samples of E′-dyad-1 (15 mg, 3.8 μmol),1-(S-acetylthio)-4-iodobenzene (1.1 mg, 3.8 μmol), Pd(PPh₃)₂Cl₂ (0.4 mg,0.6 μmol) and CuI (0.052 mg, 0.27 μmol) were reacted on a Schlenk linein the presence of toluene (3 mL) and deaeratedN,N-diisoprophylethylamine (DIEA) (0.6 mL) at 30° C. under argon for 15h with monitoring by TLC (silica, toluene) and LD-MS. The solvent wasremoved and the residue was dissolved in toluene/Et₂O (50:1).Chromatography (silica, toluene/Et₂O 50:1) afforded the title compoundas the first main band which contained a trace of the butadiyne linkeddyad. Separation by SEC (toluene) afforded the title compound as thesecond band. Removal of the solvent and washing with CH₃OH afforded ablack solid (3.5 mg, 22%). ¹H NMR δ 2.66 (s, 3H), 3.08-3.11 (s, 15H),3.27-3.60 (m, 16H), 4.95 (d, J=6.6 Hz, 5H), 5.19 (m, 1H), 5.43 (m, 2H),6.68 (d, J=7.2 Hz, 5H), 7.10 (m, 1H), 7.53 (m, 2H), 7.77 (d, J=7.5 Hz,2H), 8.09 (d, J=7.5 Hz, 2H), 8.86 (brs, 16H), 9.19 (d, J=5.7 Hz, 6H),9.66 (m, 1H), 10.05 (m, 2H), 10.25 (brs, 16H), 11.27 (brs, 16H), 12.32(m, 4H), 12.62 (m, 1H), 12.81-12.87 (m, 2H), 13.15 (brs, 16H); LD-MSobsd 4156.4 (M⁺), 4112.5 (M⁺-CH₃CO), 2981. (M⁺-(Pc)Eu(Pc)); FAB-MS obsd4150.55, calcd exact mass 4150.82 (C₂₃₃H₁₃₄OSN₄₀Eu₄); λ_(abs) 343, 418,523, 618, 722 nm.

Dyad-2. To a mixture of (Pc)Eu(Pc)Eu(E′T-Por) (18 mg, 9.0 μmol),Pd(PPh₃)₂Cl₂ (0.5 mg, 0.75 μmol), CuI (0.07 mg, 0.36 μmol) and I₂ (1.14mg, 4.5 μmol) were added toluene (3 mL) and N,N-diisopropylamine (0.6mL) and the resulting mixture was stirred at rt. The reaction progressedslowly (monitored by analytical SEC) and after 4 h the same amount ofPd(PPh₃)₂Cl₂ and CuI were added. After stirring overnight the reactionwas finished (product:starting material=96:4 based on analytical SEC).The solvent was removed. Chromatography (silica, CHCl₃) removed all thenon-triple deckers, and subsequent purification by one SEC column(toluene) gave the desired compound as a black solid after washing withCH₃OH (16 mg, 89%). ¹H NMR δ 3.04-3.07 (m, 30H), 3.27-3.41 (m, 16H),4.90 (d, J=6.6 Hz, 6H), 5.26 (m, 2H), 6.62 (d, J=7.5 Hz, 6H), 7.30 (d,J=6.6 Hz, 2H), 8.82 (brs, 16H), 9.13, (m, 6H), 9.85 (m, 2H), 10.21 (brs,16H), 11.20 (brs, 16H), 12,21 (m, 6H), 12.61 (brs, 2H), 13.08 (brs,16H); LD-MS obsd 4014.5 (M⁺); FAB-MS obsd 4014.68, calcd exact mass4014.83 (C₂₂₆H₁₃₀N₄₀Eu₄); λ_(abs) 342, 421, 522, 618, 722 nm.

EXAMPLE 2 Studies Related to the Design and Synthesis of A MolecularOctal Counter

Abbreviations herein are as follows: C₈OPc means —OC₈H₁₇Pc,2,3,9,10,16,17,23,24 (C₈H₁₇ implies n-octyl); TBuPc meanstetra-tert-butylphthalocyanine; Me₈Pc means —CH₃, 2,3,9,10,16,17,23,24;T-Por means meso-tetra-p-tolylporphyrin; PnPor meansmeso-tetrapentylporphyrin; E-PnPor means5-(4-ethynylphenyl)-10,15,20-tri-n-pentylporphyrin; I-PnPor means5-(4-iodophenyl)-10,15,20-tri-n-pentylporphyrin; EB-Por means20-[4-(2-(trimethylsilyl)ethynyl)phenyl]-5,10,15-tris[4-tert-butylphenyl]porphyrin;and E′B-Por means20-[4-ethynylphenyl]-5,10,15-tris[4-tert-butylphenyl]porphyrin.

Results and Discussion.

Triple deckers sandwich complexes for the electrochemical studies insolution. The general procedure for the preparation of heterolepticporphyrin-phthalocyanine sandwich complexes is as follows (M. Moussaviet al., Inorg. Chem. 1986, 25, 2107-2108; J. Buehler et al., Inorg.Chem. 1988, 27, 339-345.). A porphyrin is refluxed in the presence ofexcess M(acac)₃.nH₂O in 1,2,4-trichlorobenzene, affording the porphyrinM(acac) complex. Subsequent treatment with dilithium phthalocyanine withcontinued reflux results in a distribution of three triple deckercomplexes including the desired product (Pc)Eu(Pc)Eu(Por). Theporphyrins (1a,b), phthalocyanines (2a-e) and 2f naphtbalocyanine wereused in the preparation of the library of triple deckers. Thesubstituents to be examined include n-pentyl and p-tolyl on a porphyrinunit and methyl, octyloxy, butoxy, and 1-butyl on a phthalocyanine unit.Note that tetra-tert-butylphthalocyanine (2d) consisted of a mixture ofregioisomers. The porphyrins were employed as the free base ligands, andthe phthalocyanines were converted to the dilithium derivatives prior toreaction. We carried out the general reaction protocol with ninecombinations of porphyrin and phthalocyanine starting materials,affording triple-decker complexes as shown in FIG. 26.

In each case, when the Eu(acac)₃.nH₂O was used, the crude reactionmixtures were purified by column chromatography on silica gel (CHCl₃).The first fraction contained the a type triple-decker complex(Por)Eu(Pc)Eu(Por) and porphyrin monomer, which were easily separated bySEC chromatography (THF). The second and third triple-decker complexesof type b (Pc)Eu(Por)Eu(Pc) and type c (Pc)Eu(Pc)Eu(Por) requiredfurther silica column chromatography with toluene. In some cases (SeeExperimental Section below) the chromatography had to be repeatedseveral times. Reactions of phthalocyanine 2c with porphyrin 1a or 1bled to the recovery of starting materials and a very complicated mixtureof products, but triple-decker complexes were not present—presumably dueto steric hindrance caused by substituents in the1,4,8,11,15,18,22,25-positions. In the case of the reaction of porphyrin1b and phthalocyanine 2e with Ce(acac)₃.nH₂O (D. Chabach et al., New J.Chem. 1992, 16, 431-433), the a type triple decker sandwich complex wasisolated as the main product and only traces of b and c type complexeswere detected by LD-MS. The reaction of porphyrin 1b andnaphthalocyanine 2f in the presence of Eu(acac)₃.nH₂O, resulted mainlyin the recovery of starting material and very small amount of a typetriple decker. The yields of the triple deckers isolated from eachreaction are listed in Table 4.

Each triple-decker complex was characterized by LD-MS, FAB-MS, UV-Visspectroscopy and ¹H NMR spectroscopy. However, ¹H NMR spectroscopy wasnot particularly useful for the characterization of complexes containingthe tetra-tert-butylphthalocyanine ligand (6a, 6b, 6c, 9a, 9b, 9c) dueto the presence of phthalocyanine regioisomers. The purity of thecomplexes were confirmed by TLC or LD-MS analysis in the absence of amatrix. In the LD-MS spectra of 3a, 3c, 6a, 9a, other peaks in additionto the molecular ion peak M⁺ were detected and could be assigned tofragmentation: (Por)Eu(acac), (Por)Eu(Pc) or M⁺-[C₄H₉]. Type a compoundswere easily distinguished from types b and c by the significantdifference in molecular masses. Although compounds b and c have the samemolecular mass, the structure was identified from UV-Vis spectra, bycomparison to spectra reported for (Pc)Eu(Pc)Eu(Por) (J. Jiang, et al.,Inorg. Chim. Acta 1998, 268, 49-53; J. Jiang et al., Inorg. Chim. Acta1997, 255, 59-64) and for analogous cerium (III) triple-decker complexes(D. Chabach et al., New J. Chem. 1992, 16, 431-433; D. Chabach et al.,J. Am. Chem. Soc. 1995, 117, 8548-8556) [Finally, the triple-deckercomplex containing three tetra-tert-butylphthalocyanine ligands (i.e.,of general structure (Pc)Eu(Pc)Eu(Pc), 9d) was isolated as the mostpolar triple-decker sandwich complex from the reaction of 1b and 2d].

Electrochemistry. Each member of the library of triple-decker sandwichcomplexes that was pure and available in sufficient quantity wasexamined electrochemically in solution. Selected electrochemical dataare summarized in Table 5. For compounds 3c, 4a, 6a, 6b, 9a, 9c, 10a,10b four oxidation states were observed, whereas compounds 6c, 9d and 4cprovided only three oxidation states. For most complexes, two reductionprocesses were observed, though exceptions occurred with 6b, 9d and 3cwhere three reduction states were detected. The highest electrochemicalpotential was exhibited by the triple-decker complex 3c with only theelectron donating group (p-tolyl) on the periphery of the porphyrinring, whereas the lowest potential was measured for compound 10a with analiphatic chain in the porphyrin meso positions and eight methyl groupson the phthalocyanine unit. These results are consistent withexpectation based on knowledge of substituent effects.

Strategy. In order to identify combinations of triple deckers that couldbe used in the design of an octal counter, we overlaid square wavevoltammograms and inspected them visually for interleaved oxidationpotentials. Some of the pairs that exhibited very good separations ofpotentials included 9c and 6a, 3c and 9a, and 6a and 9a. Of these 9cappeared to be quite attractive for two reasons: (1) this complexexhibited very low oxidation potentials, thereby enabling the low regimeof the accessible electrochemical window on gold to be accessed; (2) wehave in hand an S-(acetylthio)-derivatized triple decker similar to thatof 6a. Therefore we designed molecule 13 (FIG. 27) which has the samesubstituents but replaces one n-pentyl group on the porphyrin with athiol-derivatized linker for attachment to a gold electrode. A number oftriple decker complexes has been prepared during the course of thisstudy.

Building blocks. The synthesis of the triple-decker sandwich molecules13 and 15 required the preparation of porphyrins 14 and 16 (FIG. 27) (B.Littler et al., J. S. J. Org. Chem. 1999, 64, 2864-2872; W.-S. Cho etal., J. Org. Chem. 1999, 64, 7890-7901). Each porphyrin has beenprepared via a rational route. The reaction of 4-bromobenzaldehyde and2,2-dimethyl-3-butyn-2-ol under Pd-coupling conditions (L. Della Cianaand A. Haim, J. Heterocyclic Chem. 1984, 21, 607-608; R. Wagner et al.,J. Org. Chem. 1995, 60, 5266-5273; R. Wagner et al., Chem. Mater. 1999,10, 2974-2983) afforded aldehyde 17 (FIG. 28) (K. Yamada et al., Chem.Lett. 1999, 895-896). This rather polar ethyne protecting group wasselected in order to facilitate separation of the porphyrin in the finalstep of the synthesis. Condensation of the latter with excess pyrrole inthe presence of trifluoroacetic acid (TFA) (B. Littler et al., J. S. J.Org. Chem. 1999, 64, 2864-2872) gave dipyrromethane 18 in 56% yieldafter chromatography followed by crystallization. The desireddipyrromethane-dicarbinol 19 was prepared in a two step process.Treatment of 5-(n-pentyl)dipyrromethane with ethylmagnesium bromidefollowed by n-hexanoyl chloride afforded the corresponding1,9-diacyldipyrromethane in good yield. Reduction of thediacyldipyrromethane with NaBH₄ in tetrahydrofiran (THF)-methanolafforded the corresponding dicarbinol 19, which was not characterizedbut was used immediately in the subsequent reaction. The reaction ofdipyrromethane 18 and dipyrromethane-dicarbinol 19 was performed in thepresence of TFA in acetonitrile followed by oxidation with2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ). Although this routeusually provides porphyrin devoid of acidolytic scrambling,dipyrromethane-dicarbinols with aliphatic substituents are known tocondense with modest scrambling. The major other porphyrin speciesidentified was meso-tetrapentylporphyrin. The polarity imparted by the2-(2-hydroxypropyl)ethyne protecting group enabled facile separation ofthe mixture and porphyrin 20 was obtained in 28% yield. Porphyrin 16 wasprepared in the same manner. Reaction of dipyrromethane 21 withdipyrromethane-dicarbinol 22 in the presence of TFA afforded porphyrin16 in 32% yield (FIG. 29).

The reaction of Eu(acac)₃-nH₂O and free base porphyrin 20 afforded thecorresponding Eu(Por)acac complex. Treatment of the latter withdilithium phthalocyanine 2d in refluxing 1,2,4-trichlorobenzene gave amixture of six triple deckers (with protected or deprotected ethynemoieties) together with residual starting materials. Since the2-(2-hydroxypropyl) ethyne protecting group is unstable under thereaction conditions forming the triple decker, ethyne deprotection wasperformed at the porphyrin stage. Furthermore, this approach minimizessynthetic manipulation of the triple deckers.

In order to obtain the deprotected ethyne, porphyrin 20 was firstmetalated with zinc (J. Rodriquez et al., J. Chem. Soc. Perkin Trans I1997, 709-714) under standard conditions giving porphyrin 23 (FIG. 30).Deprotection of the ethyne by refluxing-with sodium hydroxide in toluene(L. Della Ciana and A. Haim, J. Heterocyclic Chem. 1984, 21, 607-608)(98% yield) gave building block 24. Demetalation of 24 with TFA (J.Lindsey et al., Tetrahedron 1994, 50, 8941-8968) afforded free basemono-ethynyl porphyrin 14 in 83% yield (FIG. 30). The metalation stepwas performed in order to suppress possible decomposition of the freebase porphyrin upon exposure to sodium hydroxide. Subsequently, and toour surprise, we found that reaction of porphyrin 20 with sodiumhydroxide in refluxing toluene proceeded smoothly to give porphyrin 14in 90% yield.

The reaction of Eu(acac)₃.nH₂O and free base porphyrin 14 afforded thecorresponding Eu(Por)acac complex. Treatment of the latter withdilithium phthalocyanine 2d in refluxing 1,2,4-trichlorobenzene gave amixture of products together with residual starting materials (FIG. 31).Column chromatography on silica gel with chloroform gave four bands.Further purification of the first fraction by SEC in THF affordedtriple-decker complex 25a in 11% yield and unreacted porphyrin 14 (38%).UV-Vis spectroscopy and LD-MS analysis allowed the structure of 25a tobe assigned as (E-PnPor)Eu(tBu₄Pc)Eu(E-PnPor). The second band containedfree base phthalocyanine 2d (5%). The third and the fourth bands gavecompounds which had the same molecular mass, but displayed differentabsorption spectra. These complexes could be assigned as(tBu₄Pc)Eu(E-PnPor)Eu(tBu₄Pc) 25b (1.3%) and(tBu₄Pc)Eu(tBu₄Pc)Eu(E-PnPor) 25c (12%) in order of elution from theadsorption column.

The monoiodo-derivative triple-decker complex 26c (FIG. 31) was isolatedin 12% (40 mg) yield after two column chromatography procedures, with asmall amount of impurity still detected by LD-MS. However, the molecularmass of the impurity could not be assigned to a known triple-deckercomplex.

In the triple decker forming reaction, Eu(acac)₃.nH₂O and free baseporphyrin 16 afforded the corresponding Eu(Por)acac complex. Treatmentof the latter with lithium phthalocyanine 2a in refluxing1,2,4-trichlorobenzene gave a mixture of products together with residualstarting materials (FIG. 32). Column chromatography on silica gel withchloroform gave four bands. Further purification of the first fractionby SEC in THF afforded triple-decker complex 27a in 26% yield. UV-Visspectroscopy and LD-MS analysis allowed the structure of 27a to beassigned as (EB-Por)Eu(Pc)Eu(EB-Por) sandwich complex. The third and thefourth bands gave compounds which had the same molecular mass, butdisplayed different absorption spectra. These complexes could beassigned as (Pc)Eu(Por)Eu(EB-Pc) 27b (1.6%) and (Pc)Eu(Pc)Eu(EB-Por) 27c(9.1%) in order of elution from the adsorption column. Treatment of 27cwith K₂CO₃ (R. Wagner et al., J. Am. Chem. Soc. 1996, 118, 11166-11180)afforded the deprotected triple decker 28 in 94% yield.

Thiol-derivatized triple decker sandwich complexes. We have investigatedseveral methods for attaching the thiol handle to the triple deckerbuilding blocks. Our studies have revealed the advantages of certainapproaches and conditions for avoiding critical side reactions. Thesefindings have emerged from the three methods described below.

(1) In order to attach a protected thiol unit to the triple decker,ethynyl triple-decker 25c and 1-iodo-4-(S-acetylthio)benzene werereacted under Pd-coupling conditions in the presence of copper(I) iodide(FIG. 33) (L. Cassar, J. Organomet. Chem. 1975, 93, 253-257; H. Dieck etal., J. Organomet. Chem. 1975, 93, 259-263). Three main compounds wereobtained. Because the S-acetylthio group can undergo cleavage in thepresence of most of the commonly used bases in Pd-coupling reactions,DIEA was used instead and no cleavage product was found in the reactionmixture (R. Hsung et al., Tetrahedron Lett. 1995, 26, 4525-4528). Themixture was separated by silica column chromatography followed by SEC.Based on molecular ion peak assignments upon LD-MS analysis, thestructure of the less polar compound was assigned to a butadiyne-linkeddyad of triple-deckers (29). Homo-coupling of ethynes yielding thebutadiyne byproduct is a well-known side reaction in Sonogashirareactions in the presence of copper (K. Sonogashira et al., TetrahedronLett. 1975, 4467-4470). The second fraction contained two inseparablecompounds. The LD-MS spectrum showed two major peaks at m/z 2439 and2548. The latter corresponds to the desired S-(acetylthio)-derivatizedtriple decker 13, while the former is consistent with an acetylatedderivative of the ethynyl triple-decker starting material. We attributethe formation of the acetylated by-product to acetyl transfer from the1-iodo-4-(S-acetylthio)benzene (or product derived therefrom), giving30.

(2) The difficulties encountered in isolating the desired molecule 13prompted the investigation of a different route. The homo-coupling ofthe ethynyl-substituted triple-decker yielding the butadiyne-linked dyadis readily avoided by use of an iodo-substituted triple-decker complexas the starting material. In this case any acetylation of the ethyne dueto side reactions from the S-(acetylthio)benzene starting material wouldnot affect the integrity of the triple decker product. Furthermore theomission of copper, which promotes the oxidative coupling of triplebonds, greatly suppresses homo-coupling. Thus, compound 26c was reactedwith 1-ethynyl-4-(S-acetylthio)benzene (D. Pearson and J. Tour, J. Org.Chem. 1997, 62, 1376-1387) under mild copper-free Pd-mediated couplingconditions (R. Wagner et al., J. Org. Chem. 1995, 60, 5266-5273; R.Wagner et al., Chem. Mater. 1999, 10, 2974-2983) (triple-decker complex3 mM with molar ratio of complex—(1), ethyne compound—(1),P(o-tol)₃—(1.2) and Pd₂(dba)₃—(0.15) in toluene and DIEA (5:1) at 35°C.). After purification, unreacted starting material 35 was recovered in40% yield and the desired triple decker 13 was obtained in 14% yield(FIG. 34). Although the reaction in the absence of copper is slower, theproduct distribution is cleaner.

(3) The ethynyl-substituted triple decker (Pc)Eu(Pc)Eu(E′B-Por) 28 and4-iodo-1-(S-acetylthio)benzene were coupled under the Pd-couplingconditions (Pd₂(dba)₃, P(o-tol)₃ used for joining porphyrin buildingblocks (FIG. 35). LD-MS analysis of the crude reaction mixture revealedtwo dominant peaks (m/z 2179, 2287) corresponding to the acetylatedproduct and the desired product, respectively. Column chromatographyafforded the two separate species. ¹H NMR analysis of the former speciesrevealed a sharp singlet (2.86 ppm, 3H) consistent with an acetylmoiety. The desired S-acetylthio derivatized triple-decker 15 wasobtained in 19% yield, which is quite low compared with the typicalyield (50˜60%) in the reaction between two porphyrin monomers under thesame conditions. Thus, excluding copper from the coupling reactionavoids homo-coupling but does not suppress acetyl transfer reaction.

Conclusions. We have synthesized a library of triple-decker complexescomprised of different porphyrins and phthalocyanines substituted withvarious electron-donating substituents. Electrochemical examination ofthis library has revealed appropriate combinations of triple deckersthat may be used in the design of an octal counter. As part of thesynthesis component of this work, we have identified a suitable routefor attaching the thiol linker which should avoid some problematic sidereactions and thereby facilitate access to the desired thiol-derivatizedtriple deckers. The simplest way to avoid forming the acetylated tripledecker by-product is to employ an iodo- rather than ethynyl-substitutedtriple-decker complexes. Two thiol-derivatized triple decker complexeshave been prepared.

B. Experimental Section

General. ¹H NMR spectra (300 MHz) and absorption spectra (HP 8451A, Cary3) were collected routinely. All ¹H NMR spectra were collected in CDCl₃(300 MHz) unless noted otherwise. All absorption spectra were collectedin toluene. Porphyrin-phthalocyanine sandwich complexes were analyzed bylaser desorption (LD-MS) mass spectrometry (Bruker Proflex II) and highresolution fast atom bombardment (FAB-MS) on a JEOL (Tokyo, Japan) HX110HF mass spectrometer. LD-MS analysis was done without a matrix orwith the matrix POPOP. High resolution mass spectrometry was carried outat greater than unit resolution. Commercial sources provided dilithiumphthalocyanine (Aldrich), Eu(acac)₃.nH₂O (Alfa Aesar) and Pd(PPh₃)₂Cl₂(Aldrich). Unless otherwise indicated, all other reagents were obtainedfrom Aldrich Chemical Company, and all solvents were obtained fromFisher Scientific.

Chromatography. Adsorption column chromatography was performed usingflash silica gel (Baker, 60-200 mesh). Preparative-scale size exclusionchromatography (SEC) was performed using BioRad Bio-beads SX-1. Apreparative-scale glass column (4.8×60 cm) was packed using Bio-BeadsSX-1 in THF and eluted with gravity flow. Following purification, theSEC column was washed with two volume equivalents of THF. Analyticalscale SEC was performed with a Hewlett-Packard 1090 HPLC using a 1000Åcolumn (5 μL, styrene-divinylbenzene copolymer) with THF as eluent (0.8mL/min).

Solvents. Toluene was distilled from CaH₂, THF (Fisher, certified ACS)was distilled from sodium, and triethylamine (Fluka, puriss) wasdistilled from CaH₂. Pyrrole (Acros) was distilled at atmosphericpressure from CaH₂. All other solvents were used as received.

General procedure for the preparation of triple deckers. A mixture ofthe porphyrin (0.06 mmol) and Eu(acac)₃ nH₂O (88 mg, 0.17 mmol) in1,2,4-trichlorobenzene (13 mL) was heated to reflux and stirred underargon for 4 h. The resulting cherry-red solution was cooled to rt, thenthe dilithium phthalocyanine (0.09 mmol) was added. The mixture wasrefluxed for an additional 5 h, then the volatile components wereremoved under vacuum. The residue was dissolved in CHCl₃ and loaded ontoa silica gel column packed with the same solvent. Elution with CHCl₃afforded three main bands. The first band (brown) contained mainly thetriple-decker complex (Por)Eu(Pc)Eu(Por) and unreacted porphyrinstarting material. The second main band (olive or black) contained thetriple-decker complex (Pc)Eu(Por)Eu(Pc) in a very small amount,therefore often not isolated or characterized. The third main band (darkgreen) contained mainly the triple-decker complex (Pc)Eu(Pc)Eu(Por).

The first band collected was redissolved in THF and loaded onto a SECcolumn. Elution with the same solvent afforded (Por)Eu(Pc)Eu(Por) as thefirst band (greenish-brown), which after removal of the solvent affordeda brownish-black solid. The dark green band (third) collected wasredissolved in toluene and loaded onto a silica gel column packed withthe same solvent. Elution with toluene afforded the dark greenish-blueband containing (Pc)Eu(Pc)Eu(Por), which after removal of the solventafforded a dark green solid. Final purification of each compound will bedescribed specifically.

(T-Por)Eu(C₈OPc)Eu(T-Por) (4a). The reaction of (T-Por) (12 mg, 0.017mmol) and Li₂[(M-OC₈H₁₇)₈Pc] (40 mg, 0.026 mmol) was performed asdescribed above. Chromatography (silica, CHCl₃) then SEC of the firstband gave a greenish-brown solid. The greenish-brown solid was finallypurified by chromatography (silica, hexanes:ethyl acetate (graduallyfrom 10% to 30% ethyl acetate)) affording triple-decker complex 4a (12mg, 22%). ¹H NMR (CDCl₃) δ 1.25 (t, J=7.2 Hz, 24H), 1.7-2.0 (m, 32H),2.13 (quint, J=7.5 Hz, 16H), 2.37 (quint, J=7.2 Hz, 16H), 2.79 (m, 16H),3.11 (s, 24H), 3.36 (m, 16H), 4.29 (s, 16H), 5.17 (d, J=6.6 Hz, 8H),6.0-6.2 (m, 16H), 6.79 (d, J=6.6 Hz, 8H), 9.1-9.3 (m, 8H), 12.10 (s,8H), 12.83 (s, 8H); LD-MS obsd 3183.7; FAB-MS obsd 3179.54, calcd exactmass 3179.54 (C₁₉₂H₂₁₆N₁₆O₈Eu₂); λ_(abs) 374, 419, 496, 611 nm.

(C₈OPc)Eu(C₈OPc)Eu(T-Por) (4c). Chromatography (of the third band) onsilica eluted with a mixture of hexanes and THF (gradually from 0% to20% THF) afforded pure compound (8 mg, 10%). ¹H NMR (CDCl₃) δ 1.01 (t,J=6.9 Hz, 24H), 1.15 (t, J=7.1 Hz, 24H), 1.27 (s, 24H), 1.4-1.6 (m,32H), 1.6-1.9 (m, 72H), 1.9-2.3 (m, 48H), 2.5-2.8 (m, 32H), 3.09 (s,12H), 3.31 (brs, 12H), 4.95 (brs, 8H), 5.17 (m, 4H), 5.7-6.1 (m, 12H),6.43 (m, 8H), 6.70 (d, J=6.6 Hz, 4H), 9.31 (m, 4H), 13.12 (s, 4H); LD-MSobsd 4047.3; FAB-MS obsd 4048.3, calcd exact mass 4048.4(C₂₄₀H₃₂₄N₂₀O₁₆Eu₂); λ_(abs) 373, 423, 540, 631, 737 nm.

(T-Por)Eu(tBu₄Pc)Eu(T-Por) (6a). The reaction of (T-Por) (31 mg, 0.052mmol) and Li₂(tBu₄Pc) (45 mg, 0.078 mmol) was performed as describedabove. Chromatography (silica, CHCl₃) then SEC gave a greenish-brownsolid. The greenish-brown solid was finally purified by chromatography(silica, hexanes:ethyl acetate (gradually from 10% to 30% ethylacetate)) (7 mg, 8%). ¹H NMR (CDCl₃) δ 3.0-3.1 (m, 24H), 3.1-3.3 (m,36H), 4.07 (d, J=5.7 Hz, 16H), 4.91 (q, J=8.1 Hz, 8H), 6.5-6.7 (m, 8H),9.0-9.1 (m, 8H), 10.7-10.9 (m, 4H), 12.0-12.3 (m, 8H), 12.5-13.0 (m,8H); LD-MS obsd 2388.0, 1562.7, 1547.2, 823.4; FAB-MS obsd 2378.72,calcd exact mass 2378.83 (C₁₄₄H₁₂₀N₁₆Eu₂); λ_(abs) 362, 421, 493, 608nm.

(tBu₄Pc)Eu(tBu₄Pc)Eu(T-Por) (6c). The dark greenish-black solid obtainedfrom chromatography (toluene, as described above) was further purifiedby chromatography (silica, toluene) (19 mg, 15%). ¹H NMR (CDCl₃) wascollected though interpretation was precluded as the compound wasisolated as a mixture of inseparable regioisomers. LD-MS obsd 2449.5;FAB-MS obsd 2447.05, calcd exact mass 2446.94 (C₁₄₄H₁₃₂N₂₀Eu₂); λ_(abs)346, 417, 526, 620, 727 nm.

(Pn-Por)Eu(tBu₄Pc)Eu(Pn-Por) (9a). The reaction of (Pn-Por) (40 mg,0.017 mmol) and Li₂(tBu₄Pc) (58 mg, 0.01 mmol) was performed asdescribed above. Chromatography (silica, CHCl₃) then SEC gave agreenish-brown solid. The greenish-brown solid was finally purified bychromatography (silica, hexanes:ethyl acetate (gradually from 10% to 30%ethyl acetate)) (29 mg, 19%). ¹H NMR (CDCl₃) 0.6-0.8 (m, 16H), 0.79 (t,J=7.5 Hz, 24H), 1.19 (m, 16H), 1.45 (m, 16H), 3.52 (s, 36H), 3.7-4.0 (m,16H), 5.0-5.3 (m, 16H), 10.6-10.9 (m, 4H), 12.0-12.5 (m, 8H); LD-MS obsd2218.82, 2162.0, 2149.0; FAB-MS obsd 2217.97, calcd exact mass 2218.07(C₁₂₈H₁₅₂N₁₆Eu₂); Anal. Calcd: C, 69.30; H, 6.91; N, 10.10. Found: C,69.04; H, 6.86; N, 9.82; λ_(abs) 357,427, 502, 566, 626 nm.

(tBu₄Pc)Eu(tBu₄Pc)Eu(Pn-Por) (9c). The dark greenish-black solidobtained from chromatography (toluene, as described above) was furtherpurified by chromatography (silica, toluene) followed by againchromatography (silica, hexanes:ethyl acetate (gradually from 10% to 30%ethyl acetate)) (first band, 17 mg, 11%). ¹H NMR (CDCl₃) was collectedthough interpretation was precluded as the compound was isolated as amixture of inseparable regioisomers. LD-MS obsd 2374.0; FAB-MS obsd2366.11, calcd exact mass 2366.05 (C₁₃₆H₁₄₇N₂₀Eu₂); λ_(abs) 345, 413,527, 583, 629, 736 nm.

(tBu₄Pc)Eu(tBu₄Pc)Eu(tBu₄Pc) (9d). The dark greenish-black solidobtained from chromatography (toluene, as described above) was furtherpurified by chromatography (silica, toluene) followed by chromatographyagain (silica, hexanes:ethyl acetate (gradually from 10% to 30% ethylacetate)) (second band, 11 mg, 8%). The ¹H NMR spectrum (CDCl₃) wascollected though interpretation was precluded as the compound wasisolated as a mixture of inseparable regioisomers. LD-MS obsd 2523.1;FAB-MS obsd 2514.96, calcd exact mass 2515.04 (C₁₄₄H₁₄₄N₂₄Eu₂); λ_(abs)341, 649 nm.

(Pn-Por)Eu(Me₈Pc)Eu(Pn-Por) (10a). The reaction of (Pn-Por) (50 mg,0.085 mmol) and Li₂(Me₈Pc) (250 mg (compound used without purification),0.12 mmol) was performed as described above. Chromatography (silica,CHCl₃) then SEC gave a greenish-brown solid. The greenish-brown solidwas finally purified by chromatography (silica, hexanes:toluene(gradually from 50% to 100% toluene)) and chromatography (silica,hexanes:CH₂Cl₂ (gradually from 10% to 20% CH₂Cl₂) (7 mg, 4%), whichslowly decomposes during purification. ¹H NMR (CDCl₃) δ 0.6-0.8 (m,16H), 0.90 (t, J=6.9 Hz, 24H ), 1.2-1.5 (m, 32H), 3.8-3.9 (m, 16H), 4.24(s, 24H), 5.41 (s, 16H), 12.27 (s, 8H); LD-MS obsd 2109.2, 2051.5,2037.6; FAB-MS obsd 2106.98, calcd exact mass 2106.96 (C₁₂₀H₁₃₆N₁₆Eu₂);λ_(abs) 362, 428, 502, 567, 625 nm.

(Me₈Pc)Eu(Me₈Pc)Eu(Pn-Por) (10c). The dark greenish-black solid obtainedfrom chromatography (toluene, as described above) was further purifiedby chromatography (silica, toluene) followed by chromatography again(silica, CH₂Cl₂) (3 mg, 2%); the compound slowly decomposed duringpurification. The ¹H NMR (CDCl₃) spectrum was collected but the amountof material was insufficient to obtain a good spectrum. LD-MS obsd2143.3, 1401.7; FAB-MS obsd 2142.79, calcd exact mass 2142.81(C₁₂₀H₁₁₆N₂₀Eu₂); λ_(abs) 351, 417, 631, 652, 684 nm.

(Pn-Por)Ce(Me₈Pc)Ce(Pn-Por) (11a). A mixture ofmeso-tetrapentylporphyrin (75 mg, 0.13 mmol) and Ce(acac)₃.nH₂O (140 mg,0.32 mmol) in 1,2,4-trichlorobenzene (11 mL) was refluxed under a slowstream of argon for 24 h. After cooling, a solid sample of Li₂(Me₈Pc)(610 mg, 0.32 mmol, impure) was added and the mixture was again refluxedunder argon for 10 h. Evaporation under vacuum gave a dark green solid.The residue was dissolved in CHCl₃ and loaded onto a silica gel columnpacked with the same solvent. Elution with CHCl₃ afforded three mainbands. The first band (green-brown) contained mainly the title compoundand unreacted porphyrin starting material. The dark green band containedmainly the triple-decker complex (Me₈Pc)Ce(Pn-Por). The first bandcollected was redissolved in THF and loaded onto a SEC column. Elutionwith the same solvent afforded (Pn-Por)Ce(Me₈Pc)Ce(Pn-Por) 11a as thefirst band (greenish-brown). The greenish-brown solid was finallypurified by washing with MeOH (23 mg, 8.5%). ¹H NMR (CDCl₃) δ −4.29(brs, 16H), −2.15 (brs, 8H ), −1.44 (s, 24H), 0.51 (m, 16H), 0.58 (t,J=6.7 Hz, 24H), 0.68 (m, 16H), 3.15 (s, 16H), 3.81 (s, 16H); LD-MS obsd2090.6, 2032.7, 2019.3, 1963.6, 1949.4, 1904.0, 1890.1; FAB-MS obsd2106.98, calcd exact mass 2106.96 (C₁₂₀H₁₃₆N₁₆Eu₂); λ_(abs) 363, 427,498, 565, 615 nm.

Preparation of triple deckers upon reaction of meso-tetrapentylporphyrinand dilithium 2,3 naphthalocyanine (12a). A mixture of Pn-Por (66 mg,0.09 mmol) and Eu(acac)₃.nH₂O (140 mg, 0.28 mmol) in1,2,4-trichlorobenzene (21 mL) was refluxed under a slow stream of argonfor 4 h. After cooling, a solid sample of Li₂Nc (100 mg, 0.14 mmol) wasadded and the mixture was again refluxed under argon for 5 h.Evaporation under vacuum gave a dark green solid. The residue wasdissolved in CHCl₃ and loaded onto a silica gel column packed and elutedwith CHCl₃. The first band collected was redissolved in THF and loadedonto a SEC column. Elution with the same solvent afforded(Pn-Por)Eu(2,3Nc)Eu(Pn-Por) 12a as the first band (greenish-brown). Thegreenish-brown solid was finally purified by chromatography (silica,CH₂Cl₂/hexanes, 3:1), (5 mg, 3%). LD-MS obsd 2203.5, 2146.9, 2132.9;FAB-MS obsd 2194.89, calcd exact mass 2194.89 (C₁₂₈H₁₂₈N₁₆Eu₂); λ_(abs)330, 429, 543, 612 nm.

4-(3-methyl-3-hydroxy-1-butyn-1-yl)benzaldehyde (17).4-Bromobenzaldehyde (3.0 g, 16 mmol), Pd(PPh₃)₂Cl₂ (110 mg, 0.170 mmol)and CuI (16 mg, 0.07 mmol) were placed in a Schlenk flask. The flask wasthen evacuated and purged with argon (3 times) on the Schlenk line. Thenfreshly distilled and degassed TEA (32 mL) was added, and after purgingwith argon, 2-methyl-3-butyn-2-ol (1.90 mL, 19.4 mmol) was added. Thereaction mixture was stirred for 2 h at 40° C. (The progress of thereaction was monitored by GC-MS). The reaction mixture was evaporated todryness and then chromatographed (silica, CH₂Cl₂). Bulb-to-bulbdistillation (93-95° C., 0.001 mm Hg) gave a pale yellowish oil (2.90 g,95%). ¹H NMR (CDCl₃) δ 1.61 (s, 6H), 2.23 (brs, 1H), 7.52 (AB/2, J=8.1Hz, 2H), 7.79 (AB/2, J=8.1 Hz, 2H), 9.02 (s, 1H); ¹³C NMR δ 31.9, 66.1,81.9, 98.8, 129.8, 130.1, 132.7, 135.9, 192.3; IR (film) v (cm⁻¹) 790.4,830.1, 906.3, 963.4, 1014.3, 1046.1, 1165.9, 1207.0, 1273.4, 1303.0,1373.0, 1457.6, 1563.8, 1603.6, 1700.0, 2228.1, 2735.0, 2837.8, 2934.1,2982.2, 3413.3; MS (EI⁺) m/z 188 (M⁺, 35%), 173 (100%), 159 (10%); EI-MSobsd 188.0835, calcd exact mass 188.0837 (C₁₂H₁₂O₂).

5-[4-(3-methyl-3-hydroxy-1-butyn-1-yl)phenyl]dipyrromethane (18).Following a standard procedure, a solution of aldehyde 17 (2.5 g, 13mmol) in pyrrole (23.0 mL, 330 mmol) was treated with TFA (72 μL, 1.3mmol). Column chromatography (silica, CH₂Cl₂ gradually to CH₂Cl₂:MeOH(7.5%)) followed by crystallization from ethanol:water afforded whitecrystals (2.3 g, 56%). mp 145-146° C. ¹H NMR (CDCl₃) δ 1.62 (s, 6H),1.89 (brs, 1H), 5.46 (s, 1H), 5.89 (s, 2H), 6.17 (dd, J=5.7, 3.0 Hz,2H), 6.07 (m, 2H), 7.1-7.2 (m, 2H), 7.3-7.4 (m, 2H); ¹³C NMR δ 32.2,44.4, 66.3, 82.7, 94.5, 108.1, 109.1, 118.2, 122.0, 129.1, 132.5, 132.8,143.1; Anal. Calcd for C₂₀H₂₀N₂O: C, 78.92; H, 6.62; N, 9.20. Found: C,79.03; H, 6.69; N, 9.29.

5-[4-(3-methyl-3-hydroxy-1-butyn-1-yl)phenyl]-10,15,20-tri-n-pentylporphyrin(20). Following a standard procedure, dipyrromethane 18 (530 mg, 1.8mmol) and dipyrromethane-dicarbinol 19 [prepared directly from thediacyldipyrromethane (720 mg, 1.8 mmol) and used without purification]in CH₃CN was treated with TFA (1.6 mL, 29 mmol). Then DDQ (1.2 g, 5.3mmol) was added and the reaction mixture was stirred for 1 h. Columnchromatography on silica (toluene and CH₂Cl₂ (3:2)) gavemeso-tetrapentylporphyrin (54 mg, 5.2%) and the title compound (275 mg,23%). ¹H NMR (CDCl₃) δ −2.68 (brs, 2H), 0.9-1.1 (m, 9H), 1.5-1.6 (m,6H), 1.7-1.9 (m, 12H), 2.2-2.3 (brs, 1H), 2.4-2.6 (m, 6H), 4.8-5.0 (m,6H), 7.84 (d, J=8.1 Hz, 2H), 8.14 (d, J=7.8 Hz, 2H), 8.78 (d, J=5.1 Hz,2H), 9.37 (d, J=5.1 Hz, 2H), 9.49 (dd, J=9.6, 5.1 Hz, 4H); LD-MS obsd680.6, 623.1; FAB-MS obsd 678.4310, calcd exact mass 678.4298(C₄₆H₅₄N₄O); λ_(abs) (CH₂Cl₂) 422, 520, 554, 600, 658 nm; λ_(em)(λ_(exc) 520 nm) 661, 731 nm.

Zn(II)-5-[4-3-methyl-3-hydroxy-1-butyn-1-yl)phenyl]-10,15,20-tri-n-pentylporphyrin(23). Porphyrin 20 (50 mg, 0.07 mmol) was treated with Zn(OAc).2H₂O (1.5g, 5.0 mmol) in CH₂Cl₂:MeOH (10:1, 66 mL). The traditional workup gave apurple solid (50 mg, 91%) ¹H NMR (CDCl₃) δ 1.01 (m, 9H), 1.5-1.6 (m,7H), 1.7-1.8 (m, 6H), 1.8 (s, 6H), 2.2-2.3 (m, 2H), 2.3-2.5 (m, 4H),4.29 (t, J=8.6 Hz, 2H), 4.48 (t, J=8.0 Hz, 4H), 7.86 (AB/2, J=8.1 Hz,2H), 8.13 (AB/2, J=7.8 Hz, 2H), 8.74 (AB/2, J=5.1 Hz, 2H), 8.89 (AB/2,J=4.2 Hz, 2H), 8.90 (AB/2, J=5.7 Hz, 2H), 9.23 (AB/2, J=4.2 Hz, 2H);LD-MS obsd 742.7, 685.4; FAB-MS obsd 740.3452, calcd exact mass 740.3433(C₄₆H₅₂N₄OZn); λ_(abs) (CH₂Cl₂) 421, 553, 593 nm; λ_(em) (λ_(exc) 570nm) 560, 601, 651 nm.

Zn(II)-5-(4-ethynylphenyl)-10,15,20-tri-n-pentylporphyrin (24).Porphyrin 23 (50 mg, 0.074 mmol) was dissolved in toluene (5 mL) andpowdered NaOH (100 mg) was added. The reaction mixture was refluxed for2 h. After cooling to rt, the mixture was placed on a silica column(CH₂Cl₂:hexanes, 3:2), affording 45 mg of a purple solid (98%). ¹H NMR(CDCl₃) δ 1.0-1.1 (m, 9H), 1.4-1.9 (m, 12H), 2.1-2.2 (m, 2H), 2.3-2.5(m, 4H), 3.43 (s, 1H), 4.0-4.2 (m, 2H), 4.4-4.5 (m, 4H), 8.01 (AB/2,J=8.1 Hz, 2H), 8.22 (AB/2, J=8.1 Hz, 2H), 8.71 (AB/2, J=4.2 Hz, 2H),8.78 (AB/2, J=4.2 Hz, 2H), 8.81 (AB/2, J=5.1 Hz, 2H), 9.26 (AB/2, J=4.5Hz, 2H); LD-MS obsd 684.9, 627.5; FAB-MS obsd 682.3029; calcd exact mass682.3014 (C₄₃H₄₆N₄Zn); λ_(abs) (CH₂Cl₂) 421, 553, 593 nm; λ_(em)(λ_(exc) 570 nm) 560, 601, 651 nm.

5-(4-Ethynylphenyl)-10,15,20-tri-n-pentylporphyrin (14). A solution ofZn-porphyrin 24 (45 mg, 0.066 mmol) in CH₂Cl₂ was treated with TFA (0.56mL). The standard workup followed by chromatography afforded a purplesolid (34 mg, 83%). ¹H NMR (CDCl₃) δ −2.67 (s, 2H), 1.0-1.1 (m, 9H),1.5-1.7 (m, 6H), 1.7-1.9 (m, 6H), 2.4-2.6 (m, 6H), 3.37 (s, 1H), 4.8-5.0(m, 6H), 7.91 (d, J=7.2 Hz, 2H), 8.15 (d, J=8.1 Hz, 2H), 8.80 (d, J=5.1Hz, 2H), 9.37 (d, J=4.5 Hz, 2H), 9.47 (dd, J=8.1 Hz, 4.2 Hz, 4H); LD-MSobsd 622.2, 564.8; FAB-MS obsd 620.3886, calcd exact mass 620.3879(C₄₃H₄₈N₄); λ_(abs) (CH₂Cl₂) 420, 519, 555, 597, 657 nm; λ_(em) (λ_(exc)535 nm) 659, 728 nm.

Preparation of triple deckers upon reaction of (E-PnPor). Reaction of5-(4-ethynylphenyl)-10,15,20-tri-n-pentylporphyrin (14) (35 mg, 0.057mmol), Eu(acac)₃.nH₂O (88 mg, 0.17 mmol) and Li₂(tBu₄Pc) (49 mg, 0.09mmol) in 1,2,4-trichlorobenzene (13 mL) gave three main products aftercolumn chromatography (silica, chloroform). The first band collected wasredissolved in THF and loaded onto a SEC column. Elution with the samesolvent afforded (E-PnPor)Eu(tBu₄Pc)Eu(E-PnPor) (25a) as the first band(greenish-brown), which after removal of the solvent afforded agreenish-black solid (14 mg, 11%). ¹H NMR (CDCl₃) δ 0.85 (brs, 4H), 0.34(t, J=6.9 Hz, 6H), 0.5-1.0 (m, 28H), 1.25 (m, 8H), 1.57 (m, 8H), 2.6(brs, 4H), 3.47 (m, 38H), 3.57 (s, 2H), 4.28 (brs, 8H), 4.4-4.6 (m, 4H),4.7-4.9 (m, 6H), 5.1-5.2 (m, 4H), 5.9-6.1 (m, 4H), 6.81 (d, J=6.6 Hz,2H), 8.76 (d, J=6.6 Hz, 2H), 9.66 (d, J=5.7 Hz, 2H), 10.96 (m, 4H),12.68 (m, 8H); LD-MS obsd 2284.9, 2227.2, 2215.8; FAB-MS obsd 2278.99,calcd exact mass 2278.99 (C₁₃₄H₁₄₀N₁₆Eu₂); λ_(abs) 358, 428, 502, 566,619 nm. The third band (dark green) collected was redissolved in tolueneand loaded onto a silica gel column packed with the same solvent.Elution with toluene afforded the first band (dark greenish-blue)containing (tBu₄Pc)Eu(tBu₄Pc)Eu(E-PnPor) (25c), which after removal ofthe solvent afforded a dark green solid (16 mg, 12%). ¹H NMR (CDCl₃) wascollected though interpretation was precluded as the compound wasisolated as a mixture of inseparable regioisomers. LD-MS obsd 2403.5;FAB-MS obsd 2396.96, calcd exact mass 2397.02 (C₁₃₉H₁₄₂N₂₀Eu₂); λ_(abs)345, 419, 530, 583, 627, 733 nm.

Preparation of triple deckers upon reaction of (I-PnPor). Reaction of5-(4-iodophenyl)-10,15,20-tri-n-pentylporphyrin (100 mg, 0.14 mmol),Eu(acac)₃.nH₂O (213 mg, 0.42 mmol) and Li₂(tBu₄Pc) (120 mg, 0.21 mmol)in 1,2,4-trichlorobenzene (32 mL) gave three triple deckers. The firstband (red-brownish) collected was redissolved in THF and loaded onto aSEC column. Elution with the same solvent afforded(I-PnPor)Eu(tBu₄Pc)Eu(I-PnPor) (26a) as the first band (olive-brown),which after removal of the solvent afforded a brownish solid (28 mg,8%). ¹H NMR (CDCl₃) δ −0.81 (brs, 4H), 0.38 (t, J=6.9 Hz, 6H), 0.5-1.0(m, 24H), 1.1-1.3 (m, 8H), 1.5-17 (m, 8H), 2.05 (s, 4H), 2.6-2.7 (m,4H), 3.4-3.5 (m, 36H), 4.2-4.4 (m, 8H), 4.4-4.7 (m, 4H), 4.7-5.0 (m,6H), 5.1-5.3 (m, 4H), 5.9-6.2 (m, 4H), 7.05 (d, J=7.5 Hz, 2H), 9.01 (d,J=6.6 Hz, 2H), 9.50 (d, J=6.0 Hz, 211), 10.9-11.1 (m, 4H), 12.6-12.9 (m,8H); LD-MS (with POPOP as a matrix) obsd 2491.0, 2442.3, 2434.23,2363.73; FAB-MS obsd 2482.78, calcd exact mass 2482.78(C₁₃₀H₁₃₈N₁₆I₂Eu₂); λ_(abs) 359, 428, 501, 569, 619 nm. The third band(dark green) collected was redissolved in toluene and loaded onto asilica gel column packed with the same solvent. Elution with tolueneafforded the main band (dark greenish-blue) containing(tBu₄Pc)Eu(tBu₄Pc)Eu(I-PnPor) (26c), which after removal of the solventafforded a dark green solid (40 mg, 12%). ¹H NMR (CDCl₃) was collectedthough interpretation was precluded as the compound was isolated as amixture of inseparable regioisomers. LD-MS obsd 2508.2, 2381.7; FAB-MSobsd 2498.92, calcd exact mass 2498.91 (C₁₃₇H₁₄₁N₂₀IEu₂); λ_(abs) 345,416, 529, 583, 627, 732 nm.

Preparation of triple deckers upon reaction of EB-Por (27c). Reaction of5,10,15-tris[4-tert-butylphenyl]-20-[4-(2-(trimethylsilyl)ethynyl)phenyl]porphyrin(88 mg, 0.10 mmol), Eu(acac)₃.nH₂O (150 mg, 0.3 mmol) and Li₂Pc (80 mg,0.15 mmol) in 1,2,4-trichlorobenzene (20 mL) resulted in four bandsafter column chromatography (silica, CHCl₃). The first band(olive-brown) collected was redissolved in THF and loaded onto a SECcolumn. Elution with the same solvent afforded (EB-Por)Eu(Pc)Eu(EB-Por)(27a) as the first band (greenish-brown), which after removal of thesolvent and washing with CH₃OH afforded a greenish-black solid (34 mg,26%). ¹H NMR (CDCl₃) δ 0.62 (s, 18H), 1.89 (s, 54H), 3.83-4.03 (m, 16H),4.76 (m, 9H), 6.71 (m, 6H), 6.84 (m, 2H), 9.00 (brs, 6H), 9.19 (m, 2H),10.65 (brs, 8H), 11.46-11.60 (m, 8H), 12.73 (brs, 8H); LD-MS obsd2574.1; FAB-MS obsd 2570.90, calcd exact mass 2570.91(C₁₅₄H₁₃₆N₁₆Si₂Eu₂); λ_(abs) 355, 421, 493, 559, 606 nm.

The third band (black) collected was also redissolved in THF and loadedonto a SEC column. Elution with THF afforded (Pc)Eu(EB-Por)Eu(Pc) (27b)as the second band (black), which after removal of the solvent andwashing with CH₃OH afforded a black solid (3.5 mg, 1.6%). ¹H NMR (CDCl₃)δ 0.85 (s, 18H), 2.89, 2.94 (m, 26H), 8.05 (brs, 16H), 9.59 (brs, 16H),9.99 (m, 2H), 10.10 (m, 4H), 11.98-12.20 (m, 4H), 13.52 (m, 2H), 13.68(m, 4H); LD-MS obsd 2209.1, 2206.2; FAB-MS obsd 2206.60, calcd exactmass 2206.60 (C₁₂₅H₉₄N₂₀SiEu₂); λ_(abs) 343, 416, 519, 625, 653 nm.

The last band (green) collected was redissolved in toluene and loadedonto a short silica gel column packed with the same solvent. Elutionwith toluene afforded the first band (greenish-blue)(Pc)Eu(Pc)Eu(EB-Por) (27c), which after removal of the solvent andwashing with CH₃OH afforded a green solid (20 mg, 9.1%). ¹H NMR (CDCl₃)δ 0.68 (s, 9H), 1.86 (m, 27H), 3.20-3.29 (m, 8H), 4.71-4.91 (m, 4H),6.67 (m, 3H), 6.91 (m, 1H), 8.72 (brs, 8H), 9.08-9.16 (m, 3H), 9.41 (m,1H), 10.10 (brs, 8H), 11.10 (brs, 8H), 11.69 (m, 2H), 11.88 (m, 1H),12.16 (m, 1H), 12.97 (brs, 8H); LD-MS obsd 2117.1 (M⁺), 1181.4[M⁺-(EB-Por)Eu], 919.3 (M⁺-(Pc)Eu(Pc); FAB-MS obsd 2206.60, calcd exactmass 2206.60 (C₁₂₅H₉₂N₂₀SiEu₂); λ_(abs) 342, 417, 522, 552, 618, 721 nm.

Formation of (Pc)Eu(Pc)Eu(E′B-Por) (28). A sample of(Pc)Eu(Pc)Eu(EB-Por) (27c) (20 mg, 0.009 mmol) was treated with K₂CO₃and worked-up following the standard procedure. Column chromatography(silica, CHCl₃) afforded a black solid (18 mg, 94%). ¹H NMR (CDCl₃) δ1.96 (m, 27H), 3.30-3.38 (m, 8H), 3.71 (s, 1H), 4.77 (d, J=7.2 Hz, 3H),5.00 (d, J=6.6 Hz, 1H), 6.70 (m, 3H), 6.95 (d, J=7.2 Hz, 1H), 8.76 (brs,8H), 9.09-9.16 (m, 3H), 9.40 (m, 1H), 10.16 (brs, 8H), 11.17 (brs, 8H),11.56 (m, 2H), 11.73 (m, 1H), 12.00 (m, 1H), 13.04 (brs, 8H); LD-MS obsd2136.5 (M⁺); FAB-MS obsd 2134.56, calcd exact mass 2134.56(C₁₂₂H₈₄N₂₀Eu₂); Y_(abs) 343, 415, 522, 552, 618, 722 nm.

S-Acetylthio-derivatized triple decker (13). Route 1: Samples of(tBu₄Pc)Eu(tBu₄Pc)Eu(E-PnPor) (25c) (39 mg, 16 μmol),4-iodo-1-(S-acetylthio)benzene (44.5 mg, 0.16 mmol), Pd(PPh₃₎ ₂Cl₂ (1.7mg, 2.4 μmol) and CuI (0.22 mg, 1.1 μmol) were added to Schlenk flask.The flask was evacuated and purged with argon three times. Thendeaerated THF (6.0 mL) and deaerated DIEA (1.5 mL) were added bysyringe. The flask was immersed in an oil bath at 30° C. and stirredunder argon. The reaction was monitored by TLC (silica, toluene:Et₂O,60:1) and LD-MS. After 20 h, the solvent was removed under vacuum andthe residue was dissolved in toluene and loaded onto a silica gel columnpacked with the same solvent. Elution with toluene and thentoluene:ether (60:1) did not afford separation of products. The residuewas redissolved in THF and loaded onto a SEC column. Elution with thesame solvent afforded butadiyne-linked dyad 29 as the first band. Thetitle compound 13 was eluted as the second band together with acetylatedstarting material 30, which were not separable by any chromatographicmethod examined.

Route 2: Samples of (tBu₄Pc)Eu(tBu₄Pc)Eu(I-PnPor) (26c) (35 mg, 14μmol), 4-ethynyl-1-S-acetylthio)benzene (3 mg, 14 μmol), Pd₂(dba)₃ (2.0mg, 22 μmol) and P(o-tol)₃ (5.1 mg, 17 μmol) were added to Schlenkflask. The flask was evacuated and purged with argon three times. Thendeaerated toluene (4.6 mL) and deaerated DIEA (0.9 mL) were added bysyringe. The flask was immersed in an oil bath at 35° C. and stirredunder argon. The reaction was monitored by TLC (silica, toluene) andLD-MS. After 44 h, the solvent was removed under vacuum, the residuedissolved in toluene, and loaded onto a silica gel column packed withthe same solvent. Elution with toluene afforded the desired producttogether with a trace of unreacted starting material as the first band.The product thus obtained was further purified by a second columnchromatography procedure (silica gel, toluene), affording a black solid(13) (5.0 mg, 14%). ¹H NMR (CDCl₃) was collected though interpretationwas precluded as the compound was isolated as a mixture of inseparableregioisomers. LD-MS obsd 2550.3, 2507.8, 2495.2, 2480.2; FAB-MS obsd2547.05, calcd exact mass 2547.03 (C₁₄₇H₁₄₈N₂₀OSEu₂); λ_(abs) 339, 415,527, 577, 625, 723 nm.

S-Acetylthio-derivatized triple decker (15). Samples of(Pc)Eu(Pc)Eu(E′B-Por) (28) (15 mg, 7.0 μmol),4-iodo-1-(S-acetylthio)benzene (2.0 mg, 7.0 μmol), Pd₂(dba)₃ (1.0 mg,1.1 μmol) and P(o-tolyl)₃ (2.5 mg, 8.3 μmol) were added to a Schlenkflask. The flask was evacuated and purged with argon three times. Thendeaerated toluene (3 mL) and deaerated N,N-diisopropylethylamine (0.6mL) were added by syringe. The flask was immersed in an oil bath at 35°C. and stirred under argon. The reaction was monitored by TLC (silica,toluene) and LD-MS. After 24 h, the solvent was removed under vacuum,the residue dissolved in toluene/ether (60:1), and loaded onto a silicagel column packed with the same solvent. Elution with toluene/ether(60:1) afforded the desired product together with trace of unreactedstarting material as the first band. The product thus obtained wasfurther purified by a second column chromatography procedure (silicagel, toluene), affording a black solid (15) (3.1 mg, 19%) after removalof the solvent and washing with CH₃OH. ¹H NMR (CDCl₃) δ 1.91 (m, 27H),2.62 (s, 3H), 3.28 (m, 8H), 4.70-4.80 (m, 3H), 4.98 (d, J=6.6 Hz, 1H),6.68 (m, 4H), 6.94 (d, J=6.6 Hz, 1H), 7.54 (m, 1H), 7.71 (m, 1H), 8.03(m, 1H), 8.71 (brs, 8H), 9.05-9.12 (m, 3H), 9.42 (m, 1H), 10.10 (brs,8H), 11.11 (brs, 8H), 11.56 (m, 2H), 11.72 (m, 1H), 12.02 (m, 1H), 12.98(brs, 8H); LD-MS obsd 2291.4 (M⁺), 2250.2 (M⁺-CH₃CO), 1181.0(M⁺-(Por)Eu), 1111.6 (M⁺-(Pc)Eu(Pc)), 1067.8 (M⁺-(Pc)Eu(Pc)-CH₃CO);FAB-MS obsd 2284.59, calcd exact mass 2284.58 (C₁₃₀H₉₀OSN₂₀Eu₂); λ_(abs)341, 419, 523, 618, 721 nm.

Electrochemistry. The solution and SAM electrochemical studies wereconducted using standard instrumentation, techniques, and preparationstrategies. The solvent was CH₂Cl₂; tetrabutylammoniumhexafluorophosphate (TBAH, 0.1 M) (Aldrich, recrystallized three timesfrom methanol and dried under vacuum at 110° C.) served as supportingelectrolyte. The potentials reported are vs Ag/Ag⁺; E_(FeCp₂/FeCp₂⁺)=0.19 V.

The foregoing is illustrative of the present invention, and is not to beconstrued as limiting thereof. The invention is defined by the followingclaims, with equivalents of the claims to be included therein.

TABLE 4 Yield of triple-decker complexes. Yield Entry PorphyrinPhthalocyanine Metal Products [%] 1 1a 2a Eu 3a 12 3b 3.5 3c 26 2 1a 2bEu 4a 22 4b 7.4 4c 12 3 1a 2d Eu 6a 7.8 6b 2.7 6c 15 4 1b 2b Eu 7a 4.0 51b 2d Eu 9a 19 9c 11 9d 7.7 6 1b 2e Eu 10a 4.0 10d 2.0 7 1b 2e Ce 11a8.5 8 1b 2f Eu 12a

TABLE 5 Oxidation potentials for triple-decker complexes Com- Oxidationpotentials pound +4 +3 +2 +1 −1   −2 −3  3a  3c +1.289 +1.010 +0.623+0.223 −0.907  −1.370 −1.850  4a +1.117 +0.914 +0.529 +0.191 −1.212 −1.682  4c +0.349 +0.056 −1.173  −1.545  6a +1.267 +0.982 +0.623 +0.262−1.145  −1.651  6b +1.170 +0.932 +0.457 +0.272 −1.115  −1.444 −1.810  6c+1.014 +0.564 +0.133 −1.029  −1.508  9a +1.211 +0.850 +0.443 +0.031−1.291  −1.773  9c +1.264 +0.888 +0.447 +0.086 −1.090  −1.514  9d +0.955+0.431 +0.136 −0.944  −1.410 −1.819 10a +1.19 +0.83 +0.42  0.00 10c+1.17 +0.82 +0.36 +0.013 11a +1.147 +0.725 +0.429 +0.037 12a +1.071+0.781 +0.345 −0.126

What is claimed is:
 1. An article of manufacture, comprising: asubstrate; and a polymer bound to said substrate, said polymercomprising a plurality of covalently joined monomeric units, each ofsaid monomeric units comprising an independently selected sandwichcoordination compound; each of said sandwich coordination compoundsselected from the group consisting of double-decker sandwichcoordination compounds and triple-decker sandwich coordinationcompounds.
 2. The article of manufacture of claim 1, said substratecomprising a material selected from the group consisting of conductors,semiconductors, insulators, and composites thereof.
 3. The article ofmanufacture of claim 1, said substrate comprising a material selectedfrom the group consisting of metals, metal oxides, organic polymers, andcomposites thereof.
 4. The article of manufacture of claim 1, each ofsaid coordination compounds selected from the group consisting ofheteroleptic sandwich coordination compounds and homoleptic sandwichcoordination compounds.
 5. The article of manufacture of claim 1,wherein said polymer is covalently linked to said substrate.
 6. Thearticle of manufacture of claim 1, wherein said polymer is covalentlylinked to said substrate by thiol linkers.
 7. The article of manufactureof claim 1, wherein said article is an electrochromic display.
 8. Thearticle of manufacture of claim 1, wherein said article is a molecularcapacitor.
 9. The article of manufacture of claim 1, wherein saidarticle is a battery.